Post-wet Season Research Articles

Variation of mercury in 4 major estuaries in the Gulf of Thailand during wet season

The Mae Klong River (MK), Tha Chin River (TC), Chao Phraya River (CP), and Bang Pakong River (BPK) are recognized as critical conveyors of terrestrial substances, including pollutants, into the Inner Gulf of Thailand (Inner GOT). This study sought to explore the presence of mercury (Hg), a highly toxic and bioavailable pollutant, in both water and surface sediment at the mouths of the four rivers in pre- and post-wet season (WS). The results revealed that the total mercury (T-Hg) concentrations in the water ranged from 10 ng/L (TC) to 125 ng/L (CP) in pre-WS and 17 ng/L (MK) to 1011 ng/L (TC) in post-WS. Notably, the post-WS concentrations of T-Hg were relatively higher than the pre-WS, with an average concentration of particulate Hg (P–Hg) increasing by approximately 3–5 times. Consequently, the average P–Hg proportion to T-Hg of each estuary in the post-WS was comprised of greater than 67%. Moreover, a correlation was observed among salinity, total suspended solid (TSS) and particulate Hg (P–Hg). Similarly, the estuarine sediment, excluding MK, exhibited a higher average concentration of T-Hg during the post-WS period. The average T-Hg concentration in sediment ranged from 17 (BPK) to 119 (MK) μg/kg in pre-WS and 15 (MK) to 140 (CP) μg/kg in post-WS. The presence of organic matter (total organic carbon or TOC content), and clay-sized particles were identified as potential factors influencing the concentration of T-Hg in the sediment. In addition, a higher positive correlation was observed between T-Hg and silt-sized particles in BPK. In this study, both T-Hg in the water column and T-Hg in sediment increased during the post-WS period, suggesting that Hg transportation from sources to river mouths during WS were intensified. Furthermore, the correlation between T-Hg and fine-grained particle, as well as the greater T-Hg levels in the estuarine sediment, indicates that Hg may be transported from rivers to the offshore marine environment via the fine-grained fraction.

Restoring fish habitat values on a tropical agricultural floodplain: Learning from two decades of aquatic invasive plant maintenance efforts

Coastal managers are increasingly challenged with implementing expensive restoration and on-going maintenance programs to reinstate the services and values of floodplains as important fish nursery areas, but access to long-term data to assist with supporting success is lacking. An environmental levy (funded by farmers, Burdekin Shire Council, a local Natural Resource Management group, and Lower Burdekin Water Board) was enacted in 2003 to fund (approximately $20,000/yr AUD) an ongoing aquatic weed removal program (consisting of an aquatic plant weed harvester that removes floating vegetation to a nearby truck for composting in conjunction with boat weed spraying) designed to maintain the delivery of irrigation water as well as promoting productive fish habitat. We repeated a fish and water quality survey first performed in 2001/2002 (September 2017, May 2018) at 10 lagoons (three clear and seven turbid) on the Burdekin floodplain (north Queensland, Australia) to examine whether these maintenance efforts continue delivering the initial values set nearly 20 years ago. A total of 2267 fish from 24 species were caught, May 2018 (post-wet season) survey yielded more fish (24 species) than the September 2017 (late dry season) survey (19 species) which is close to the results of the 2001/02 survey (post-wet season, 17 species; late dry season, 16 species). A Hydrolab (September 2017) revealed that turbid and clear water lagoons had a similar rhythmic diel temperature cycle that posed no thermal risks to fish. Dissolved oxygen had distinct diel periodicity, with clear lagoons having the widest range, reaching established critical minimum thresholds for some floodplain fish, while turbid lagoons were generally less variable (presumably due to less oxygen demand from biological activity). While as long as sugarcane production occurs, excessive nutrients will necessitate continuance of the aquatic weed program; therefore, the funding model in place must remain. This study advocates the need for long-term maintenance programs facilitated by long-term partnerships, and serves as an exemplar model for managers looking to restore coastal floodplains but are challenged with persistent aquatic weed management issues, not only in Australia but also on floodplains elsewhere.

Input of plastic debris in an urban tropical river system

Land-based sources contribute approximately 80% of anthropogenic debris in marine environments. A main pathway is believed to be rivers and storm-water systems, yet this input is rarely quantified. We aimed to quantify the abundance of land-based debris entering a river system through storm drains in an urban area of tropical Australia. To account for seasonal variability, debris was quantified pre, post and during the wet season from 2014 to 2017. Plastic items within the river were compared to those in adjacent parks to assess similarities in debris composition. A total of 27,943 items were collected (92% plastic). Debris loads in the post-wet seasons were significantly higher than the wet-season. Furthermore, variability in the portion of debris found in nearby parks compared to the river suggests that factors other than rainfall, play a role in debris abundance. These results can be used to identify targeted management strategies to reduce debris loads.

Soil Quality for Rice Productivity and Yield Sustainability under Long-term Fertilizer and Manure Application

ABSTRACTProductivity and sustainability of rice-rice cropping system depend upon the soil quality which is primarily governed by application of fertilizers and manures. However, such information is limited and hence, the present investigation was carried out in a 9-year-old long-term fertilizer experiment at Bhubaneswar, India. There were seven treatments (control, application of 100% NPK, 150% NPK, 100% NPK + Zn, 100% NPK + FYM, 100% NPK + Zn + B, and 100% NPK + Zn + S) laid out in randomized block design with four replications. Indicators of soil quality (physical, chemical, and biological) were diagnosed from 30 numbers of soil properties measured on the post-wet season soil and soil quality was assessed taking productivity and sustainability of dry season rice as goal functions. Results revealed that the highest productivity and sustainability of dry season rice was found with application of 100% NPK + FYM. This treatment, in general, showed better physical, chemical, and biological properties than rest of the treatments. The highest soil quality index (SQI) was recorded in 100% NPK + FYM (0.941) treatment followed by 150% NPK (0.826) with CEC diagnosed as the only key indicator for rice productivity. For yield sustainability in dry season, reserve K and total N were important contributing 89% and 11%, respectively to the SQI. Therefore, these soil properties could be used to monitor soil quality in wet season. Application of FYM along with 100% NPK could sustain the productivity of dry season rice by improving soil properties under subtropical rice-rice system.

Long-term surface water changes and driving cause in Xiong’an, China: from dense Landsat time series images and synthetic analysis

China’s government statement recently reported the plan of constructing Xiong’an New Area, which aims to phase out some extra capital functions from Beijing and to explore an innovative urban development mode with the priority in eco-environmental protection. The New Area is located in the semi-arid North China Plain (NCP) and is home to NCP’s largest natural freshwater wetland, Baiyangdian Lake. A comprehensive realization of surface water dynamics would be crucial for policy-makers to outline a sustainable environment development strategy for New Area. In this study, we used a total of 245 time slices of cloud-free Landsat images to document the continuous changes of water bodies within Xiong’an City during 1984–2016 and to provide detailed evidence of water presence and persistency states and changes under the influences of climate change and human actions. Our results reveal that the New Area water body areas varied dramatically during the past 33 years, ranging from 0.44 km2 in April 1988 to 317.85 km2 in February 1989. The change of surface water area was not characterized by a monotonically decreasing tendency. The evolution processes can be divided into four sub-stages: the first extreme desiccation in mid-1980s, the wet stage with the most extensive inundation areas and strong inter-annual fluctuations from late-1988 to late 1999, another desiccation stage in early 2000s, and the overall recovering stage between 2007 and 2016. We also mapped the maximum water inundation extents and frequencies of all-season, pre-wet season (February-May) and post-wet season (September-December) for the 33 years and different sub-periods. Although there is good agreement between time series of surface water area evolution in the New Area and station-based precipitation and evaporation variations, multiple lines of evidences reviewed in previous research indicate that the degraded Baiyangdian Lake was also tightly associated with human activities from various aspects, including dam construction, groundwater extraction, agricultural irrigation, etc. We highlighted the current status of exploring the driving mechanism of surface water changes and existing problems, and then offer recommendations.

What influences the home range size of free-roaming domestic dogs?

In many regions of the world domestic dogs are free roaming and live in close relationship with humans. These free-roaming domestic dogs (FRDD) can cause public health problems such as dog bites and transmission of infectious diseases. To effectively control diseases transmitted by FRDD, knowledge on the dogs' behaviour is required. To identify predictors of home range (HR) size, we collected global positioning system data from 135 FRDD living in eight Aboriginal and Torres Strait Islander communities in Northern Australia. The core HR size ranged from 0·17 to 2·33 ha and the extended HR size from 0·86 to 40·46 ha. Using a linear mixed effect model with a Restricted Maximum Likelihood approach, the dog's sex and reproductive status were identified as predictors of roaming. Non-castrated males had the largest HRs, followed by neutered females. Also, FRDDs were found to roam further during the pre- than the post-wet season. These findings have implications for infectious disease spread. Identification of risk groups for disease spread within a population allows for more targeted disease response and surveillance. Further investigation of predictors of roaming in other FRDD populations worldwide would increase the external validity of such studies.

Modelling catch per unit effort of the Black Volta near the Bui dam in Ghana

AbstractThe chlorophyll a concentration and water level of the Black Volta near the Bui dam were studied in relation to fish production as measured by catch per unit effort (CPUE) between February 2011 and December 2012. The primary objective was to develop a simple linear regression model for predicting CPUE levels. The mean estimated CPUE for 2011 and 2012 was lower (6.23 kg canoe−1 day−1) in the postwet season than in the dry season (10.86 kg canoe−1 day−1) with a mean of 7.95 kg canoe−1 day−1. Hence, the dry season was the most important season for fish catches in the study area. Predictor variables that significantly explained CPUE levels were chlorophyll a (positive correlation) and water level (negative correlation) (P = 0.0002). The model was validated with independent data from the same Black Volta in 2011 and 2012. This model, CPUE = (0.062 × chlorophyll a) − (0.456 × water level) + 3.363, explained 91% CPUE variability. Independent validation indicated that the model had the potential to predict CPUE (as a measure of fish production) in the Black Volta near the Bui dam. Hence, the model is also a valuable tool to predict future trends in the CPUE levels of the Black Volta.

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Summary Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/sampling periods have only recently been developed. Here, stable isotope‐based Bayesian community‐wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar. Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010–2011 wet season. Trophic length, estimated based on δ15N, varied between 3·6 (Ambila) and 4·7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4‐dominated) had lower trophic diversity than the Zambezi and Rianila (C3‐dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season. The comparative analysis of community‐wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large‐scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.

Toxic (aluminum, beryllium, boron, chromium and zinc) in groundwater: health risk assessment

The objective of this study is to determine the seasonal water quality variations of the major springs of the Yarmouk Basin (YB) of north Jordan. A total of 36 water samples were collected in October 2006 (dry season) and in May 2007 (wet season) and analyzed for temperature, hydrogen ion concentration, electrical conductivity, aluminum, beryllium, boron, chromium and zinc. The hydrogen ion concentration was found in the alkaline ranges (7.01–7.87) and (7.01–8.09) for the pre and post-wet season water samples, respectively. Electrical conductivity varied from 300 to 1199 μS/cm and from 424 to 962 μS/cm for the dry and wet season water samples, respectively. The results of heavy metals analysis indicated that some water samples exceeded the Jordanian Standards for drinking water. Overall, the results showed that the water springs of the Yarmouk Basin in north Jordan is contaminated with heavy metals that might affect human health as well as the health of the ecosystem.

Buttresses induced habitat heterogeneity increases nitrogen availability in tropical rainforests

Role of buttresses as a physical support to trees is well known, however, information on how buttresses form habitat heterogeneity and increase availability of nitrogen (N) in tropical rainforests is not yet much known. This study reports consequence of buttresses induced habitat heterogeneity on build up and supply of mineral N in a tropical rainforest of the South Andaman Islands of India. Treatment included buttresses (upslope) and adjacent (flat) microhabitats. Mineral N ( NH 4 + N and NO 3 - N) and microbial biomass carbon (MB-C) pools and mineral N supply rate (net nitrification and net soil N mineralization rates) were measured in both microhabitats for consecutive 12 months representing wet, post wet and dry seasons. Buttress microhabitats accumulated 7 t ha −1 yr −1 litters, which was 62% higher than adjacent microhabitats. The buttress microhabitats also had 13% more fine soil particles than adjacent microhabitats. Soil organic carbon (SOC), total N, mineral N and MB-C were 18%, 52%, 38% and 34%, respectively higher in the buttress than adjacent microhabitat. However, C/N ratio was lower in the buttress (18) than adjacent microhabitat (23). Net nitrification as well as net soil N mineralization rate was 45% and 44%, respectively higher in the buttress than adjacent microhabitat. High amount of rainfall during wet season reduced the net nitrification rate and NO 3 - N pool, but increased NH 4 + N pool; these phenomena probably protected mineral N from leaching losses and enhanced the habitat heterogeneity further. Net nitrification rate, net soil N mineralization rate and MB-C were inversely correlated to the rainfall amount. However, net soil N mineralization rate was positively correlated to MB-C. These observations suggest that buttresses accelerate nitrogen cycling at microhabitat scale and form habitat heterogeneity on a landscape scale (forest floor), which forms pockets of mineral N reserves and simultaneously increases supply of plant available N in the tropical rainforests.

A comparison of spatially explicit landscape representation methods and their relationship to stream condition

Summary 1. Biodiversity, water quality and ecosystem processes in streams are known to be influenced by the terrestrial landscape over a range of spatial and temporal scales. Lumped attributes (i.e. per cent land use) are often used to characterise the condition of the catchment; however, they are not spatially explicit and do not account for the disproportionate influence of land located near the stream or connected by overland flow. 2. We compared seven landscape representation metrics to determine whether accounting for the spatial proximity and hydrological effects of land use can be used to account for additional variability in indicators of stream ecosystem health. The landscape metrics included the following: a lumped metric, four inverse-distance-weighted (IDW) metrics based on distance to the stream or survey site and two modified IDW metrics that also accounted for the level of hydrologic activity (HA-IDW). Ecosystem health data were obtained from the Ecological Health Monitoring Programme in Southeast Queensland, Australia and included measures of fish, invertebrates, physicochemistry and nutrients collected during two seasons over 4 years. Linear models were fitted to the stream indicators and landscape metrics, by season, and compared using an information-theoretic approach. 3. Although no single metric was most suitable for modelling all stream indicators, lumped metrics rarely performed as well as other metric types. Metrics based on proximity to the stream (IDW and HA-IDW) were more suitable for modelling fish indicators, while the HA-IDW metric based on proximity to the survey site generally outperformed others for invertebrates, irrespective of season. There was consistent support for metrics based on proximity to the survey site (IDW or HA-IDW) for all physicochemical indicators during the dry season, while a HA-IDW metric based on proximity to the stream was suitable for five of the six physicochemical indicators in the post-wet season. Only one nutrient indicator was tested and results showed that catchment area had a significant effect on the relationship between land use metrics and algal stable isotope ratios in both seasons. 4. Spatially explicit methods of landscape representation can clearly improve the predictive ability of many empirical models currently used to study the relationship between landscape, habitat and stream condition. A comparison of different metrics may provide clues about causal pathways and mechanistic processes behind correlative relationships and could be used to target restoration efforts strategically.

Soil N mineralization and microbial biomass carbon affected by different tillage levels in a hot humid tropic

Tillage is known to reduce soil organic carbon (SOC) and increase soil N mineralization, but information on the level of tillage that increases net soil N mineralization and simultaneously maintains a considerable amount of SOC is poorly known. This study investigated the effect of four levels of tillage (15-cm deep by a local made plough) on net soil N mineralization rate (NMR), net nitrification rate (NNR), pools of NO 3 −-N and NH 4 +-N, and microbial biomass carbon (MB-C), water content of soil (WCS) and soil temperature (ST) in a Dystric fluvisols in the hot humid tropical climate of South Andaman Island of India. We hypothesized that: (1) tillage would increase NMR and reduce amount of SOC. But, these changes would depend on frequency of the tillage, i.e. greater would be the tillage frequency; higher, the NMR and decline in the amount of SOC; (2) low tillage would increase NMR, but reduce SOC nearly equal to short term zero tillage. Tillage levels included: (1) long term zero till (not tilled from 1983 to 2002; then from 2003 to 2006 crops (maize–okra rotation) were sown by dibbling, and weeds were cut and mulched), (2) frequent till (tilled three times before each crop sowing in the crop rotation from 1983 to 2002 and 2003 to 2006 as well; weeds were removed), (3) low till (not tilled from 1983 to 1999; then tilled once before each crop sowing in the crop rotation from 2000 to 2002 and weeds were removed; from 2003 to 2006 tilled like 2000–2002, but weeds were uprooted and buried in situ), and (4) short term zero till (from 1983 to 2002 tillage history was the same as in the low till; from 2003 to 2006 the crops were sown by dibbling in the crop rotation and weeds were cut and mulched in situ). Maize ( Zea mays L.) was cultivated during wet season (WS, May to October) and okra ( Abelmoschus esculentus L.) during post-wet season (PWS, November to January) in all tillage treatments. Soils were sampled in all tillage treatments (levels) across the WS, PWS and dry (DS, February to April) seasons over two annual cycles (2004–2005 and 2005–2006) and analyses were done for the parameters investigated. We found that WCS was the highest (44–48%) during the WS and the lowest (10–16%) during the DS, however, ST was the lowest (25.5–26.5 °C) during the WS and the highest (30.5–33.4 °C) during the DS in all tillage treatments. Across the tillage levels, NMR increased from 1.06 to 1.96 μg g −1 day −1 and NNR from 1.21 to 1.88 μg g −1 day −1, and pools of NO 3 −-N and NH 4 +-N from 3.98 to 11.1 μg g −1 and 24.76 to 42.51 μg g −1, respectively. The increase was, however, the highest in the frequent till and the lowest in the long term zero till treatment. The NMR and NNR were the lowest (0.53–0.93 μg g −1 day −1 and 0.49–0.86 μg g −1 day −1, respectively) during the WS and the highest (1.09–1.71 μg g −1 day −1 and 1.06–1.61 μg g −1 day −1) during the PWS in all tillage treatments. The NMR was positively correlated with the MB-C in all tillage treatments. Concurrent with the increase in the NMR, the SOC declined in all tillage treatments, but the decline was the highest in the frequent till and the lowest in the long term zero till treatment. Across the tillage treatments, the MB-C was correlated to the SOC. The SOC in the low till (7.9 mg g −1) treatment was nearly equal to that in the short term zero till treatment (8.8 mg g −1), but NMR was higher (0.86 μg g −1 day −1) particularly during the WS when plant's demand for N is usually high. Our results supported both the hypotheses, and suggested that low tillage might be a good option for soil fertility maintenance and carbon stock build-up in the soils of the hot humid tropics.

Importance of freshwater flow in terrestrial–aquatic energetic connectivity in intermittently connected estuaries of tropical Australia

δ13C was used to identify seasonal variations in the importance of autochthonous and allochthonous sources of productivity for fish communities in intermittently connected estuarine areas of Australia’s dry tropics. A total of 224 fish from 38 species were collected from six intermittently connected estuarine pools, three in central Queensland (two dominated by C3 forest and one by C4 pasture) and three in north Queensland (one dominated by C3 and two by C4 vegetation). Samples were collected before and after the wet season. Fish collected in the two forested areas in central Queensland had the lowest δ13C, suggesting a greater incorporation of C3 terrestrial material. A seasonal variation in δ13C was also detected for these areas, with mean δ13C varying from −20 to −23‰ from the pre- to the post-wet season, indicating a greater incorporation of terrestrial carbon after the wet season. Negative seasonal shifts in fish δ13C were also present at the pasture site, suggesting a greater dependence on carbon of riparian vegetation (C3Juncus sp.) in the post-wet season. In north Queensland, terrestrial carbon seemed to be incorporated by fish in the two C4 areas, as δ13C of most species shifted towards slightly heavier values in the post-wet season. A two-source, one-isotope mixing model also indicated a greater incorporation of carbon of terrestrial origin in the post-wet season. However, no seasonal differences in δ13C were detected for fish from the forested area of north Queensland. Overall, hydrologic connectivity seemed to be a key factor in regulating the ultimate sources of carbon in these areas. It is therefore important to preserve the surrounding habitats and to maintain the hydrologic regimes as close to natural conditions as possible, for the conservation of the ecological functioning of these areas.

Seasonal dynamics of mineral N pools and N-mineralization in soils under homegarden trees in South Andaman, India

Agroforestry trees are now well known to play a central role in the build up of nutrients pools and their transformations similar to that of forest ecosystem, however, information on the potential of homegarden trees accumulating and releasing nitrogen (mineralization) is lacking. The present study reports seasonal variations in pool sizes of mineral N (NH4+-N and NO3−-N), and net N-mineralization rate in relation to rainfall and temperature under coconut (Cocos nucifera L.), clove (Eugenia caryophyllata Thunb) and nutmeg (Myristica fragrans Houtt. Nees) trees in a coconut-spice trees plantation for two annual cycles in the equatorial humid climate of South Andaman Island of India. Concentration of NH4+-N was the highest during wet season (May–October) and the lowest during post-wet season (November–January) under all the tree species. On the contrary, concentration of NO3−-N was the lowest in the wet season and the highest during the post-wet season. However, concentrations of the mineral N were the highest under the nutmeg and the lowest under the coconut trees. Like the pool sizes, mean annual mineralization was the highest under the nutmeg (561 mg kg−1 yr−1) and the lowest under the coconut trees (393 mg kg−1 yr−1). Rate of mineralization was the highest during the post-wet season and the lowest during the dry season (February–April) under all the tree species. High rainfall during the wet season, however, reduced the rate of nitrification under all the tree species. The mean annual mineralization was logarithmically related with rainfall amount and mean monthly temperature.

The effect of impoundments on the structure and function of fish fauna in a highly regulated dry tropics estuary

Ross River flows through the Townsville/Thuringowa urban area in north Queensland, Australia, which has a dry tropical climate characterized by high inter-annual rainfall variation. Unregulated rivers in the Ross catchment basin deliver freshwater flows to their estuaries during both strong and weak wet seasons. The construction of a series of dams and weirs on Ross River means the wet-dry cycle is accentuated, leading to constant marine salinities throughout the estuary becoming the norm, with a lack of freshwater flow for five or more years at a time. The fish fauna of Ross River estuary was sampled in the post wet and dry seasons during an extremely dry climatic period (1994) and extremely wet climatic period (2000) using a small mesh (6 mm) pocket seine net. The fish fauna seemed to reflect seasonal differences. Catches from 1994 (dry period) were comprised entirely of 88 marine and euryhaline species, while the 69 species captured in 2000 (wet period) included 13 freshwater species. However, the freshwater species in the upper estuary were individuals washed over the weir, rather than part of a functional faunal gradient. During 1994 faunal composition was related more to site identity than to the position of the site along an upstream gradient. In contrast, during 2000 there were clear upstream faunal gradients with compositions in upstream sites heavily influenced by freshwater species, and marine and euryhaline species dominating downstream sites. Patterns of species dominance also varied between years. In contrast, trophic composition showed consistent shifts in both years, from high proportions of herbivores, carnivores and benthoplanktivores in May towards high proportions of benthivores in August. Not only do faunal composition, seasonal faunal change and ecological connectivity seem to be impaired, but ecological processes in the estuary that rely on seasonal freshwater flows are likely to be unable to operate normally in most years. The extreme seasonality in Ross River may serve as a model for many of the changes that will be experienced in dry tropics estuaries under global climate change scenarios of more extreme seasonality.

Coherent patterns of abundance and size of a tropical snapper in dynamic estuary systems

Although tropical estuaries are important juvenile habitats for the snapper, Lutjanus russelli, the extent of this utilisation, and relationships to physical variation are unknown. We used fish trapsto investigate spatial and temporal patterns of distribution, abundance and size of L. russelli within and between three tropical estuaries (Cattle, Barramundi and Alligator Creeks) over a two year period. L. russelli showed no indication of spatial segregation by size along the lengths of the estauries. The probability of capturing L. russelli was similar throughout Barramundi Creek and the seaward parts of Cattle Creek. However, the probability of capture fell markedly in upstream regions of Cattle Creek. These areas where characterised by depressed salinity levels due to seasonal flooding. High probabilities of capture of L. russelli during the wet and post-wet seasons in the whole of Barramundi Creek correlated with the time of smallest modal sizes. Thisreflected the entry of large numbers of small recruits into the trappable population. Temporal patterns in mean length were consistent for both years. The major feature of the size data was a clear pattern of seasonal change in the mean fork length of L. russelli, with largest mean sizes occurring in the pre-wet and the smallest mean sizes in the wet and post-wet seasons. This pattern probably reflected the interaction of four processes; the entry of new recruits into the trappable population, growth and mortality during residence in the estuarine nursery habitats, and migration of large fish away from the estuaries. The three creeks studied provided L. russelli with a harsh and extremely variable environment. Over the three creeks, salinities ranged from extremely hyposaline (0‰) to very hypersaline (55.5‰) and varied up to 39‰ within a location. However, despite the substantial physical differences and the spatial separation of the three estuaries, the patterns of temporal change were clear and consistent. Overall, the annual pattern of change insize seemed to relate more to biological processes of recruitment, mortality and migration than to responses to physical variability.

Optimization of aquatic-terrestrial ecosystem in relation to soil nitrogen status for the cultivation of fish and aquatic food crops of the Indian subtropics.

A case study was undertaken during wet and postwet seasons to improve the perennial and alternate submerged saucer-shaped ponded lands (tal and semi-tal lands) in the coasts and northeastern plains of the Indian subtropics through pisciculture and cultivation of starch- and protein-rich aquatic food crops like water chestnut (Trapa bispinosa Roxb.) and makhana or fox nut (Euryale ferox Salisb.). The study revealed that the physico-chemical properties of soils (pH, organic C, organic matter, available N, P, and K) as well as quality of water (pH, EC, BOD, COD, CO3+, HCO3-, NO3-N, SO4-S, and Cl-), growing fish, makhana, and water chestnut was remarkably influenced by different moisture regimes and exhibited a significant improvement of soil health. The amount of organic C, available N, P, and K content were found significantly highest in the treatment where makhana was grown under alternate flooding and drying situation with a depth >2 m as compared to other treatments. Such enrichment of soil fertility, particularly in available N and P content, might be due to the accumulation of considerable amounts of biomass and fish excreta and their subsequent decomposition in situ in the soils. Therefore, the present study suggests that the N-enriched soil may effectively be utilized further for growing subsequent arable crops surroundings during summer season, which not only saves the amount of applied N fertilizer but also increases the apparent N efficiency with simultaneous increase in yield, and would benefit the farmers in this region.

Southern oscillation and the northern australian prawn catch

Associations are established between the southern oscillation index (SOI) and penaeid prawn catches within the northern Australian prawn fishery. Analysis involved calculation of correlations between Gulf of Carpentaria banana prawn andtiger prawn catches and Troup’s SOI. Significant positive correlations are observed between catch size and SOI for specific months from pre-wet to post-wet seasons. For banana prawns, the results indirectly confirm some earlier observations of increased catches in conjunction with high rainfall during the onset of monsoon periods, but also indicate an association with late rains. However, the relationship with tiger prawns appears to be in the opposite direction, showing negative correlations with SOI for particular months. Some hypotheses are suggested to explain these results in terms of environmental effects on spawning populations, and comment is made on the potential for forecasting catch sizes.

Epibenthos of mangrove waterways and open embayments: Community structure and the relationship between exported mangrove detritus and epifaunal standing stocks

The epibenthos inhabiting creek-bottoms in a tidally influenced mangrove forest, a mangrove-lined estuary and several sites in two open embayments, was sampled on four occasions between August 1986 and June 1987. The inshore (mangrove habitats)-offshore (embayment) patterns in total faunal taxonomic richness (means ranging from 0 to 32·5 taxa per trawl) and density (range of means, −2 ) were generally complex, with patterns across the gradient changing seasonally. Patterns in total biomass (range of means 0–740 mg.m −2 ) were clearer, with highest biomasses recorded in May (post-wet season) and lowest in February (mid-wet season), with no significant cross-habitat gradient in biomass. Densities and biomasses were lower than those recorded in other studies, probably owing to the physically harsh conditions available to epibenthos and to the low quality of mangrove detritus as a food source. The significant difference in the structure of epibenthic communities in mangrove and embayment habitats in the dry season months (August and October) was likely due to the longer residence time of water in mangrove water-ways at that time of the year. Greater tidal amplitudes and increased tidal current velocities in February transported mangrove detritus and many faunal taxa into embayments. Variation in the quantities of exported mangrove detritus in nettings explained significant proportions of the variance in total (and component taxa) epibenthic standing stocks in mangrove and embayment habitats. Several factors may be important in causing the positive response of different groups within the epibenthos to mangrove detritus. For penaeid shrimps it seems likely that clumps of exported mangrove detritus provide refuges from predatory fish in both mangrove and embayment habitats.

Protein-energy malnutrition in northern Sudan: prevalence, socio-economic factors and family background

The socio-economic and family background and the nutrition of 145 children with kwashiorkor admitted to hospital in Khartoum over a 2-year period were compared with 113 marasmic kwashiorkor, 158 marasmic, and 186 nutritionally normal controls of similar age. Peak admissions for kwashiorkor were in the wet and post-wet season and the mean (SD) age was 1.6 (0.6) months. Mothers of malnourished children were more likely to be pregnant, and had poorer housing, sanitation and water supply, a lower income and food expenditure and less education than controls. Mothers of controls breastfed their children longer, introduced mixed feeding earlier, offered a wider variety of foods, and were more likely to have had their infants immunized. Neither family instability nor cultural practices which result in separation of children from their mothers appear to have an important role in protein-energy malnutrition in the Sudan. Families of kwashiorkor children had a higher food expenditure and better maternal education than marasmic children. There was no significant difference between the two groups in duration of breastfeeding or in the age of introduction of mixed diet. However, kwashiorkor children appeared to be offered more meat. Differences in food availability could account for the relative retardation of growth and lack of subcutaneous fat in marasmus compared to kwashiorkor.