Seasonal Water Bodies Research Articles

Increasing hypoxia in the Changjiang Estuary during the last three decades deciphered from sedimentary redox-sensitive elements

Ranked as one of the world's largest seasonal hypoxic water bodies (Dissolved oxygen, DO≤2 mg l−1), the Changjiang hypoxia has been reported to grow rapidly worse in recent decades according to cruise observations, but it has been seldom studied by sedimentary records. In this paper, four gravity cores (E1-E4), retrieved from the Changjiang Estuary, were dated by excess 210Pb and analyzed with grain-size compositions, total organic carbon (TOC) contents, and RSEs (redox sensitive elements) compositions. We aim to decipher RSEs enrichment characteristics and controlling mechanisms in the Changjiang Estuary. The results show that Mo and V enrichment is highly promoted by particle absorption and FeMn redox cycling at the shallow estuarine environment (E1 and E2) with occasional hypoxic disturbances. Scavenging of Mo and V by organic complexation becomes significant at the hypoxic center (E3), together with great influence by FeMn redox cycling, but they do not work effectively for U enrichment because of its easy remobilization and abundant riverine input. Moreover, upcore increasing trends of Mo, V, and U in E3 match well with a general lowering trend of bottom water DO minima since the mid-1980s. There are two progressive hypoxic development stages intercalated with a less DO-depleted period 1991–1997 as shown by both cruise observations and RSEs/Al records. These findings are vital to better understanding coastal hypoxic development and RSEs enrichment mechanisms in the seasonal hypoxic settings, because hypoxia is predicted to increase in the near future due to intensifying human disturbances.

Application of satellite altimetry in understanding river–wetland flow interactions of Kosi river

Flood-plain wetlands are the seasonal water bodies formed along a river. These wetlands become active during the monsoon season, which frequently grow in size with seasonal floods and eventually dry up during the non-monsoon season. The flow interaction between flood-plain wetlands and the river sometimes vary over a very short period in response to rapid rise in the river water level due to high precipitation in its upstream catchment. Understanding the complex flow interactions between the river and its associated flood-plain wetlands with field-based measurements of wetland hydrologic characteristics is always a challenging task. To overcome these challenges, an attempt has been made to utilise Topex/Poseidon satellite altimetry-derived water levels into a hydrodynamic model (HEC-RAS) to study river and wetland flow interactions in the lower reach of the Kosi river in India. The satellite altimetry-derived water levels and Landsat satellite images on the Kosi wetlands are used to develop volume-elevation relation. HEC-RAS is setup over the study area and calibrated for different values of manning’s roughness coefficient (n) for the river bank and the main channel of the river for the period of 1993–1996. Unsteady flow simulations are carried out for different monsoon seasons to simulate daily river flow interaction (inflow/outflow) between river and wetlands. Statistical analysis is performed between the altimetry-derived and the model-simulated water levels. It is found that simulated water levels are in good agreement ( $$R^{2}=0.87$$ , root mean square error of 0.84 m and Nash–Sutcliffe efficiency coefficient of 0.85) with altimetry-derived water levels. The analysis of simulations indicates that interactions between the wetland and the river are bidirectional with most of the flow coming out from the river during the month of August and leaving out from the wetlands during the month of September. The wetlands respond in three different ways, i.e., (i) gaining stage, (ii) wetland and river in equilibrium and (iii) loosing stage, which is reflected on water levels of the river and wetland. This study demonstrates complex interaction processes happening between the Kosi river and its surrounding wetlands.

Impact of land use land cover change on ecosystem services: a comparative analysis on observed data and people\u2019s perception in Inle Lake, Myanmar

BackgroundA healthy wetland provides a range of goods and services contributing to human wellbeing. Inle Lake, the first Biosphere Reserve in Myanmar, has been supporting the local inhabitants with ecosystem services (ES) including habitat for a wide range of biodiversity. In the recent years, influenced by land use land cover change (LULCC), the lake has witnessed changes with altered flow of ES, affecting human well-being. Communities’ perceptions are often undermined, when it comes to research LULCC. We analyzed LULCC change data from 1989–2000 to 2000–2014 using Landsat imageries. This was then linked to ES considering dependency through qualitative data collated from participatory rural appraisal tools and structured questionnaires focusing on people’s perception to understand the LULCC dynamics and its implication.ResultsDuring 25 years (1989–2014), there has been a sharp reduction of 164 km2 perennial wetland area in the Inle Lake, which is 4.2-fold higher in 2014 to that of 1989. Similarly, forest area has been declined by 92 km2 (8.56%) in last 25 years. Contrary to this, cropland area showed an increment of 60.67% in 2000 and 64.53% in the year 2014 alone giving a total increase by 268 km2 over the last 25 years and an expansion of 40 km2 seasonal freshwater area were observed showing periodic increment over the time. Communities from the three study areas, namely, Kyaung Taung, Zay Gon and Kyar Taw are found to have high dependence in their surrounding ecosystems. These villages utilizes 17 ES from forest ecosystem, 13 from agro-ecosystem, 10 from seasonal and 4 from perennial water body for their livelihood respectively. Around 93% of the respondents opined that forest ecosystem has decreased over the last 10 years. Around 40% of the respondents reflected an increase in area used for cropland; 43% conversely perceived a declination. About 63% of the respondents perceived such changes have brought huge reduction in availability of freshwater ES. A significant number of respondents (92%) perceived an enormous reduction in seasonal water body during the dry season.ConclusionObserved decreasing trends in forest and perennial wetland areas were consistent with people’s perceived changes. Communities associate loss of forest and wetland area with reduced availability of ES as well as degraded health of the lake.

Comparison of elemental concentration in near-surface late Holocene sediments and precipitation regimes of the Yucatán Peninsula (Mexico): a preliminary study

Paleoclimate research in the Yucatán Peninsula of Mexico has mainly involved fossil pollen preserved in sedimentary archives whilst geochemistry has received limited attention. In this study, we compared concentrations of K, Ti, Fe, Ca and Sr in 35 near-surface late Holocene sediments collected from different permanent and seasonal water bodies across the peninsula with mean annual precipitation of 600-1600 mm in order to explore the relationship between concentrations of inorganic elements and precipitation. The calcareous provenance has a diluting effect and sediments have less K, Ti and Fe (associated with clastics) and more Ca and Sr (associated with carbonate and evaporite) compared to the Upper Continental Crust. Individual elements and ratios of K/Ca, Ti/Ca and Fe/Ca in samples with minimal clastics did not show any relationship with precipitation. Average values of elemental ratios in sediments with more clastics increase as the mean annual precipitation increases. However, the sampling protocol and presence of most of the sampled water bodies being in a single precipitation cluster (i.e. 1200-1400 mm/year) did not allow a complete evaluation of the potential correlation between precipitation and elemental ratios. Considering that the concentration of Ti is low in sediments of the limestone-rich Yucatán Peninsula and Fe is mobile in anoxic depositional environments, the K/Ca ratio can be used as a preliminary proxy to evaluate precipitation in sedimentary records.

Quillworts from the Amazon: A multidisciplinary populational study on Isoetes serracarajensis and Isoetes cangae.

Isoetes are ancient quillworts members of the only genus of the order Isoetales. The genus is slow evolving but is resilient, and widespread worldwide. Two recently described species occur in the Eastern Brazilian Amazon, Isoetes serracarajensis and Isoetes cangae. They are found in the ironstone grasslands known as Canga. While I. serracarajensis is present mostly in seasonal water bodies, I. cangae is known to occur in a single permanent lake at the South mountain range. In this work, we undertake an extensive morphological, physiological and genetic characterization of both species to establish species boundaries and better understand the morphological and genetic features of these two species. Our results indicate that the morphological differentiation of the species is subtle and requires a quantitative assessment of morphological elements of the megaspore for diagnosis. We did not detect differences in microspore output, but morphological peculiarities may establish a reproductive barrier. Additionally, genetic analysis using DNA barcodes and whole chloroplast genomes indicate that although the plants are genetically very similar both approaches provide diagnostic characters. There was no indication of population structuring I. serracarajensis. These results set the basis for a deeper understanding of the evolution of the Isoetes genus.

Present status, problems and prospect of fish farming at Gazipur Sadar upazila in Bangladesh

The present study was conducted to reveal the present scenario, problems and the prospect of fish farming of Gazipur Sadar upazila Bangladesh. The primary data were collected through field survey, questionnaire interview and focus group discussion from the fish farmers of several villages and urban areas of the upazila. Secondary data were collected from the Department of Fisheries and aquaculture extension section. Gazipur Sadar upazila has 14462.42 ha potential fisheries resources of which floodplains, seasonal water bodies, and ponds comprise 71.01%, 13.04%, and 8.57%, respectively. The total fish production of the upazila in 2016-17 was 14492.7 MT, 27% of the Gazipur district. The highest fish production of 5436 MT and 4.39 MT/ha/year came from the pond sector. Among different pond culture systems, the semi-intensive system had the highest fish production output (2826 MT). Exotic carps were the highest produced fish in the ponds. However, in spite of comprising a huge proportion of seasonal floodplains the fish production from this sector was only 0.42 MT/ha/year in 2016-2017. This indicates the poor utilization of inland open water resources for fish production in the study area. The major areas were identified to improve the existing pond fish farming situation were access to low-interest loan, quality seed, supply of advanced technologies, need-based training, and marketing facilities. Along with improving the pond fish farming, community-based fisheries management and some aquaculture initiatives on private own seasonal floodplains should be taken on a priority basis to improve open water management and to flourish inland fish production in the study area.Progressive Agriculture 29 (1): 53-63, 2018

MAPPING WETLANDS OF DONGTING LAKE IN CHINA USING LANDSAT AND SENTINEL-1 TIME SERIES AT 30M

Abstract. Mapping and monitoring wetlands of Dongting lake using optical sensor data has been limited by cloud cover, and open access Sentinal-1 C-band data could provide cloud-free SAR images with both have high spatial and temporal resolution, which offer new opportunities for monitoring wetlands. In this study, we combined optical data and SAR data to map wetland of Dongting Lake reserves in 2016. Firstly, we generated two monthly composited Landsat land surface reflectance, NDVI, NDWI, TC-Wetness time series and Sentinel-1 (backscattering coefficient for VH and VV) time series. Secondly, we derived surface water body with two monthly frequencies based on the threshold method using the Sentinel-1 time series. Then the permanent water and seasonal water were separated by the submergence ratio. Other land cover types were identified based on SVM classifier using Landsat time series. Results showed that (1) the overall accuracies and kappa coefficients were above 86.6 % and 0.8. (3) Natural wetlands including permanent water body (14.8 %), seasonal water body (34.6 %), and permanent marshes (10.9 %) were the main land cover types, accounting for 60.3 % of the three wetland reserves. Human-made wetlands, such as rice fields, accounted 34.3 % of the total area. Generally, this study proposed a new flowchart for wetlands mapping in Dongting lake by combining multi-source remote sensing data, and the use of the two-monthly composited optical time series effectively made up the missing data due to the clouds and increased the possibility of precise wetlands classification.

Aliens are moving to the Arctic frontiers: an integrative approach reveals selective expansion of androgenic hybrid Corbicula lineages towards the North of Russia

Increases in human activity and climate change are factors that are expected to augment the number and impact of alien species in the northern regions. In the present paper, we report the discovery of a population of Asian Corbicula clams in the North of Russia near the Arctic frontier (64°N, 40°E), which is the most northern record of these invaders in the world. This population contains two distinct lineages that are living in sympatry in a man-made channel of the Arkhangelsk thermal power plant. The first lineage belongs to the morphotype Rlc by shell morphology but reveals the FW5 mtDNA haplotype (COI and 16S rRNA genes), which was typically recorded in the morphotype R. The second lineage reveals the shell morphological pattern of the morphotype R but has the FW17 mtDNA haplotype, which usually occurs in specimens of the morphotype S. Both forms that were identified, based on conchological and anatomical features and differences in mtDNA haplotypes, reveal the same 28S rDNA sequences but show intragenomic nDNA variability with two different variants of the 28S rDNA gene within each individual (allelic sequence heterogeneity). The discrepancy between mtDNA data and shell morphology could be explained by the well-known mechanism that is associated with androgenesis together with “egg parasitism” (mitochondrial genome-capture) in invasive Corbicula clams. The intragenomic 28S rDNA variability may be due to a hybridization event which can join different alleles from the two diploid (or polyploid) parental taxa to an allopolyploid descendant. We found that the lineages that rarely occur in European populations are exclusively established in a population near the Arctic frontier. Moreover, specimens belonging to the R-morphotype with the FW17 mtDNA haplotype that has sporadic occurrences in central Europe is prevalent (> 90% of a total sample) in a mollusk assemblage at the studied site in northern Russia. Additionally, we show that the life span of Corbicula clams in high latitudes may be longer than 1 year. Isolated Corbicula populations in artificially heated or geothermal reservoirs may therefore be primary sources for a broad invasion to seasonal waterbodies of the high-latitude regions in the future as climate warming progresses.

Geoarchaeological Investigation of Site Formation and Depositional Environments at the Middle Palaeolithic Open-Air Site of ‘Ein Qashish, Israel

‘Ein Qashish is a Middle Palaeolithic open-air site in the southern Levant, encompassing an excavated area of several hundred square meters and a 4.5-m thick stratigraphic section. Its placement within a fluvial system, combined with the presence of Neanderthal skeletal remains and diverse material culture finds, presents possibilities for understanding human behaviour on the open landscape during the late Middle Palaeolithic. The aim of this study is to investigate the depositional and post-depositional processes at ‘Ein Qashish, based on the stratigraphic section exposed in the 2013 excavation season. We employed field observations, sedimentology, micromorphology, mineralogy, elemental and isotopic analyses. Our results indicate that the sedimentary sequence, including four archaeological occupation levels, accumulated in a generally low-energy alluvial environment with evidence for syn-depositional localised seasonal water bodies. On-going post-depositional processes related to wetting and drying cycles include shrink-swell and calcite and gypsum pedofeatures. Bone mineral is relatively well preserved. The data suggest limited fluvial and argilliturbation reworking of artefacts, indicating that spatial patterning of lithic and bone assemblages is rather well preserved in some areas. The current analyses do not indicate the presence of combustion features or fire-related residues at the site, although burned lithics occur in low frequencies. The absence of combustion features in the large excavated area and deep stratigraphy contrasts with patterns observed in Middle Palaeolithic cave occupations in the region, adding nuance to a dataset that will enable a better understanding of human activities under sheltered and open-air conditions.

Effect of Monoculture and Polyculture Systems on Growth and Production of Fishes in Seasonal Waterbodies of <i>Haor</i> Villages, Sunamganj District

The study was conducted to assess the growth and production of Thai sarpunti (Puntius gonionotus), tilapia (Oreochromis niloticus) and rui (Labeo rohita) under monoculture and polyculture systems in seasonal waterbodies of haor environment. Selected waterbodies were divided into three treatments as T1 (sarpunti), T2 (sarpunti+tilapia) and T3 (sarpunti+tilapia+rui). Each treatment had three replicates and same stocking density (40,000 ha-1) of fishes was maintained in all treatments. Stocked fishes were fed with rice bran and wheat flour as supplemental feed at a decreasing rate of 10-5% of total biomass for twice daily. The highest final weight of sarpunti (122.32 g), tilapia (102.58 g) and rui (140.0 g) was obtained in T1, T2 and T3, respectively. Significantly higher production of sarpunti was secured in T1 (3,446.13 kg ha-1) than T2 (2,942.6 kg ha-1) and T3 (2,804.1 kg ha-1), and tilapia production was better in T2 (2,786.07 kg ha-1) than T3 (2,172.52 kg ha-1). Combined production of sarpunti, tilapia and rui was significantly (p<0.05) higher in T3 (8,341.41 kg ha-1) followed by T2 (5,728.67 kg ha-1) and T1 (3,446.13 kg ha-1). Therefore, polyculture practice of sarpunti, tilapia and rui may be suggested to disseminate at farmers’ level for boost up fish production.

Life history strategies of annual killifish Millerichthys robustus (Cyprinodontiformes:Cynolebiidae) in a seasonally ephemeral water body in Veracruz, México

The annual life cycle of Millerichthys robustus is described from an ephemeral pool in Veracruz, Mexico. The state of the pool can be divided into three periods: a flood period lasting from September to March when the pool was filled with water, a drought period from April to June when the pool was dry, and a humid period in July and August when the pool was intermittently filled. Soil substrate was examined in each of these three periods (flood, drought and humid), embryos were found, and the stage of embryonic diapause was determined. During the flood period embryos were in diapause I; during the drought period in diapause II; and during the humid period mainly in diapause III with a small subset in diapause II (an example of a bet-hedging strategy). Two hatching periods (separated by two weeks) were documented during the beginning of the flood period. Fish growth was analyzed in both males and females, with females showing an overall slower growth rate and smaller adult size. In females, ovarian maturity was characterized histologically to understand the reproductive cycle. The onset of sexual maturity began during the third week after hatching (21 days) with the presence of secondary sexual characteristics in females and the beginning of Secondary Growth Stage in some ovarian follicles. All stages of oogenesis, postovulatory follicles and ovulated oocytes were observed from the fourth week post hatching (28 days) until death. M. robustus appears to exhibit similar patterns of embryonic diapause compared to other annual killifish living in seasonal water bodies closer to the equator. This study characterizes (for the first time) the adaptations and life cycle of M. robustus. This information could be useful to evaluate the potential risk of these populations and, if necessary, to develop plans for their conservation.

Multi-species farming of major and minor carps for enhancing fish production in freshwater aquaculture

An year long experimental multi-species farming of Indian major carps (IMC) and minor carps was conducted with varied stocking densities in 15 earthen ponds (0.08 ha) to develop a suitable farming model. The IMC group included Catla catla, Labeo rohita and Cirrhinus mrigala at 35:40:25 ratio while minor carp and barb (MCB) group included Puntius gonionotus, Labeo fimbriatus and Puntius sarana at 40:35:25 ratio. Fingerlings were stocked in five density combinations (treatments) as: T1 - IMC at 8000 ha-1, T2 - IMC at 8000 ha-1 + MCB at 4000 ha-1, T3 - IMC at 4000 ha-1 + MCB at 4000 ha-1, T4 - IMC at 4000 ha-1 + MCB at 8000 ha-1 and T5 - MCB at 16000 ha-1. Survival of all species in both groups showed inverse relation with their stocked densities. T4 with IMC and MCB at 4,000 and 8,000 fingerlings ha-1, respectively, formed the ideal density with 28.8 and 76.0% higher yield realisation compared to T1 with only IMC and T5 with only MCB group, respectively. All multispecies treatments having MCB group as major component yielded higher fish biomass than those with IMC group. Such results indicated potential of multispecies farming system to increase production in seasonal ponds and water bodies retaining lower water level.

Multi-species farming of major and minor carps for enhancing fish production in freshwater aquaculture

An year long experimental multi-species farming of Indian major carps (IMC) and minor carps was conducted with varied stocking densities in 15 earthen ponds (0.08 ha) to develop a suitable farming model. The IMC group included Catla catla, Labeo rohita and Cirrhinus mrigala at 35:40:25 ratio while minor carp and barb (MCB) group included Puntius gonionotus , Labeo fimbriatus and Puntius sarana at 40:35:25 ratio. Fingerlings were stocked in five density combinations (treatments) as: T1 - IMC at 8000 ha-1, T2 - IMC at 8000 ha-1 + MCB at 4000 ha-1, T3 - IMC at 4000 ha-1 + MCB at 4000 ha-1, T4 - IMC at 4000 ha-1 + MCB at 8000 ha-1 and T5 - MCB at 16000 ha-1. Survival of all species in both groups showed inverse relation with their stocked densities. T4 with IMC and MCB at 4,000 and 8,000 fingerlings ha-1, respectively, formed the ideal density with 28.8 and 76.0% higher yield realisation compared to T1 with only IMC and T5 with only MCB group, respectively. All multispecies treatments having MCB group as major component yielded higher fish biomass than those with IMC group. Such results indicated potential of multispecies farming system to increase production in seasonal ponds and water bodies retaining lower water level.

LONG-TERM MONITORING OF WATER DYNAMICS IN THE SAHEL REGION USING THE MULTI-SAR-SYSTEM

Abstract. Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak’s water dynamics to delineate permanent and seasonal water bodies, using weather- and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSARX, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

LONG-TERM MONITORING OF WATER DYNAMICS IN THE SAHEL REGION USING THE MULTI-SAR-SYSTEM

Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak’s water dynamics to delineate permanent and seasonal water bodies, using weather- and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSARX, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

Alien Invasive Aquatic Plant Species in Botswana: Historical Perspective and Management

Aquatic ecosystems in Botswana have been under threat by the aquatic alien invasive plant species viz., salvinia Salvinia molesta Mitchell, water lettuce Pistia stratiotes L., and water hyacinth Eichhornia crassipes (Mart.) Solms-Laub. While salvinia has been termed the major threat to the Botswana wetlands, water lettuce and water hyacinth are considered to be of minor importance. This review presents the species biology, distribution, historical spread, negative impacts, control achieved right from their discovery in the country by referring to their control and management in the world. Having infested the Kwando-Linyanti-Chobe Rivers in the 1970s, salvinia was initially tried by the use of herbicides, paraquat and glyphosate, between 1972 and 1976. With the discovery of the host specific biological control weevil Cyrtobagous salviniae Calder and Sands in 1981, the weevil was introduced by Namibians on Kwando and Chobe Rivers in 1983 and by Botswana in 1986 in the Okavango Delta. While the control was slowly establishing in Kwando-Linyanti-Chobe Rivers, it became apparent that lakes and perennial swamps within and outside Moremi Game Reserve of the Okavango Delta were infested with salvinia from 1992 onwards. With continuous and sustained liberation of the weevil in the Kwando-Linyanti-Chobe Rivers and in the Okavango Delta between 1999 and 2000, salvinia control was achieved by 2003, and since then the weevil constantly keeps the weed at low levels. The success is mainly due to sustainable monitoring through the application of physical and biological control methods. However, salvinia is still threatening the Okavango Delta due to factors such as tourism activities, boat navigation fishing and transporttion by wild animals. The first occurrence of water lettuce was recorded on Kwando and Chobe Rivers in 1986. Its biocontrol weevil Neohydronomous affinis Hustache was released in the year 1987. The weevil became extinct in Selinda Canal and Zibadianja Lake on Kwando River due to dry and wet events for over 10 years and the weed had been under control biologically on Chobe River. Having surface covered the Selinda and a part of the Zibadianja in high flood and rainfall in 1999/2000 season, research was undertaken to contain water lettuce, which led to its eradication by 2005. Regular physical removal of the water lettuce prior to fruit maturity is an effective method of control or eradicating the weed in seasonal water bodies. The Limpopo Basin (shared by Botswana, South Africa, Zimbabwe and Mozambique) has become vulnerable to water hyacinth infestation. Water hyacinth infested the trans-boundary Limpopo River in 2010 sourced from Hartbeesport Dam on Crocodile River in South Africa. Botswana and South Africa have been consulting each other to implement integrated control of the weed jointly in the Limpopo River. Water hyacinth could be a continuous threat to the dams and the rivers in the Limpopo basin if its control is not taken seriously. These three species are found growing in Botswana in a range of pH between 4.5 and 10.3 and in the range of conductivities between 20 and 580 µS cm-1. Range of soluble nitrates, phosphates and potassium in the habitats of salvinia infestations were 0.02 to 1.5, 0.01 to 1.78 and 0.3 to 6.92 mg L-1 respectively. Water lettuce infestation in the seasonal Selinda Canal had a maximum of 4.7 mg L-1 nitrates, 2.8 mg L-1 phosphates and 7.9 mg L-1 potassium. Nevertheless, these three nutrients were in the range of 0.41 to 9.56 mg L-1, 0.2 to 2.9 mg L-1, and 7.7 to 11.53 mg L-1 respectively in the Limpopo River where water hyacinth infestations were observed. These nutrients were considerably high during decomposition phase of biological control of weeds. The Government of Botswana “regulates the movement and importation of boats and aquatic apparatus, to prevent the importation and spread of aquatic weeds both within and from the neighboring countries” by “Aquatic Weed (Control) Act” implemented in 1986. These measures, combined with communities, conservation groups, NGOs and public awareness campaigns, have highlighted the gravity of aquatic weeds spreading into wetlands, dams and other water bodies. In conclusion, the Government of Botswana is committed and supportive through the Department of Water Affairs in protecting the wetlands of the country efficiently and prudently.

Multi-sensor mapping of West African land cover using MODIS, ASAR and TanDEM-X/TerraSAR-X data

Land cover information plays an elementary role for regional water and land management, and is an essential variable for the assessment of ecosystem services and regional climate impact. This paper describes the generation of a regionally optimized land cover dataset for West Africa with a spatial resolution of 250m, which is based on earth observation data from three optical and radar instruments. The choice of sensors is based on their individual strengths and weaknesses in assessing specific land surface types. Annual profiles of the optical Moderate Resolution Imaging Spectroradiometer (MODIS) are analyzed for the classification of vegetated classes including agriculture. The classification approach builds on random forest classification with learning data extracted from higher resolution land cover maps. Envisat Advanced Synthetic Aperture Radar (ASAR) Wide Swath (WS) time series are used, in combination with MODIS data, to delineate permanent and seasonal water bodies. Here, an approach integrating threshold classification and morphological operations is applied. Built-up areas of different densities are identified based on a seamless coverage of radar imagery collected by the satellites TanDEM-X and TerraSAR-X. The detection of settlements is based on an unsupervised classification scheme which exploits texture metrics and backscattering amplitudes of the fine resolution radar sensors. The accuracy assessment of the multi-sensor land cover map yields an overall accuracy of 80% at legend level 1 (9 classes) and 73% at the more detailed legend level 2 (14 classes). Comparisons with available wall-to-wall datasets of the region demonstrate the valuable information content of the presented West African land cover map.

Geophytes of northern Western Ghats (Sahyadri Ranges) of India: a checklist

The geophytes in the northern Western Ghats are a significant component of the herbaceous flora, both in terms of abundance and diversity, and comprise approximately 10% of plant species. About 186 geophytic taxa were here recorded from northern Western Ghats of India during the present work. Of them, 62 geophytes are known only from northern Western Ghats. At least 22 plant families exhibit this life form. In the study region, geophytes have adapted to a monsoon seasonality. They sprout new foliage with the onset of monsoon rain in June and complete their life cycle in October when monsoon rains halt. Many of them produce flowers during the vegetative growing season but some charismatically flowers in summer season (April–May), often without leaves. A few taxa have abandoned their geophytic habit and grow in seasonal water bodies, and possess leaves without stomata and non-buoyant seeds.

On the Bennelongia barangaroo lineage (Crustacea, Ostracoda) in Western Australia, with the description of seven new species

The ostracod genus Bennelongia De Deckker & McKenzie, 1981 is endemic to Australia and New Zealand. Extensive sampling in Western Australia (WA) revealed a high specific and largely undescribed diversity. Here, we describe seven new species belonging to the B. barangaroo lineage: B. timmsi sp. nov., B. gnamma sp. nov., B. hirsuta sp. nov., B. ivanae sp. nov., B. mcraeae sp. nov., B. scanloni sp. nov. and B. calei sp. nov., and confirm the presence of an additional species, B. dedeckkeri, in WA. For five of these eight species, we could construct molecular phylogenies and parsimonious networks based on COI sequences. We also tested for cryptic diversity and specific status of clusters with a statistical method based on the evolutionary genetic species concept, namely Birky’s 4 theta rule. The analyses support the existence of these five species and a further three cryptic species in the WA B. barangaroo lineage. The molecular evidence was particularly relevant because most species described herein have very similar morphologies and can be distinguished from each other only by the shape, size and position of the antero-ventral lapel on the right valve, and, in sexual populations, by the small differences in shape of the hemipenes and the prehensile palps in males. Four species of the WA B. barangaroo lineage occur in small temporary rock pools (gnammas) on rocky outcrops. The other four species are mainly found in soft bottomed seasonal water bodies. One of the latter species, B. scanloni sp. nov., occurs in both claypans and deeper rock pools (pit gnammas). All species, except for B. dedeckkeri, originally described from Queensland, have quite clearly delimited distributions in WA. With the seven new species described here, the genus Bennelongia now comprises 25 nominal species but several more await formal description.

Evaluation of seasonal water body extents in Central Asia over the past 27 years derived from medium-resolution remote sensing data

In this study medium resolution remote sensing data of the AVHRR and MODIS sensors were used for derivation of inland water bodies extents over a period from 1986 till 2012 for the region of Central Asia. Daily near-infrared (NIR) spectra from the AVHRR sensor with 1.1km spatial resolution and 8-day NIR composites from the MODIS sensor with 250m spatial resolution for the months April, July and September were used as input data. The methodological approach uses temporal dynamic thresholds for individual data sets, which allows detection of water pixel independent from differing conditions or sensor differences. The individual results are summed up and combined to monthly composites of areal extent of water bodies. The presented water masks for the months April, July, and September were chosen to detect seasonal patterns as well as inter-annual dynamics and show diverse behaviour of static, decreasing, or dynamic water bodies in the study region. The size of the Southern Aral Sea, as the most popular example for an ecologic catastrophe, is decreasing significantly throughout all seasons (R2 0.96 for April; 0.97 for July; 0.96 for September). Same is true for shallow natural lakes in the northern Kazakhstan, exemplary the Tengiz-Korgalzhyn lake system, which have been shrinking in the last two decades due to drier conditions (R2 0.91 for July; 0.90 for September). On the contrary, water reservoirs show high seasonality and are very dynamic within one year in their areal extent with maximum before growing season and minimum after growing season. Furthermore, there are water bodies such as Alakol-Sasykol lake system and natural mountainous lakes which have been stable in their areal extent throughout the entire time period. Validation was performed based on several Landsat images with 30m resolution and reveals an overall accuracy of 83% for AVHRR and 91% for MODIS monthly water masks. The results should assist for climatological and ecological studies, land and water management, and as input data for different modelling applications.