Natural Reference Conditions Research Articles

Assessment of the ecological status of large lowland rivers (Sava and Tisa, Serbia) based on digital microscopic investigation of the diatom communities

Large lowland rivers represent an important type of ecosystem that has been under a constant anthropogenic influence (industry, thermal power plants, untreated communal water, and agriculture) for centuries, which has led to most of them no longer meeting natural reference conditions. These pressures affect diatom communities which represent a reliable bioindicator of the overall degradation of water bodies. The current study provides detailed information about benthic diatoms from the large international lowland rivers Sava and Tisa, analyzed using digital microscopy. Using the digital method and the BIIGLE 2.0 image annotation system, a total of 205 and 206 diatom taxa in the Sava and Tisa rivers were identified, belonging to 65 and 63 genera, respectively. Some of the dominant genera in the Sava River were Achnanthidium, Cocconeis, Gyrosigma, and Navicula, while in the Tisa River, mostly centric diatoms (Discostella, Cyclotella, Stephanodiscus) were dominant. Most of the recorded species are alkaliphilic and characteristic of running waters with high trophic conditions. The presence of halophilic taxa was also noted (e.g. Bacillaria paxilifera, Tryblionella species, Nitzschia clausii, Navicula salinarum). These taxa are sensitive indicators of even short-term changes in lowland lotic ecosystems characterized by elevated conductivity. The diatom indices showed very consistent ecological status, mainly moderate in terms of the general pollution index IPS, and poor to bad ecological status according to trophic diatom indices (Rott TI and TDI).

Land use diversification may mitigate on-site land use impacts on mammal populations and assemblages.

Land use is a major cause of biodiversity decline worldwide. Agricultural and forestry diversification measures, such as the inclusion of natural elements or diversified crop types, may reduce impacts on biodiversity. However, the extent to which such measures may compensate for the negative impacts of land use remains unknown. To fill that gap, we synthesised data from 99 studies that recorded mammal populations or assemblages in natural reference sites and in cropland and forest plantations, with or without diversification measures. We quantified the responses to diversification measures based on individual species abundance, species richness and assemblage intactness as quantified by the mean species abundance indicator. In cropland with natural elements, mammal species abundance and richness were, on average, similar to natural conditions, while in cropland without natural elements they were reduced by 28% and 34%, respectively. We found that mammal species richness was comparable between diversified forest plantations and natural reference sites, and 32% lower in plantations without natural elements. In both cropland and plantations, assemblage intactness was reduced compared with natural reference conditions, but the reduction was smaller if diversification measures were in place. In addition, we found that responses to land use were modified by species traits and environmental context. While habitat specialist populations were reduced in cropland without diversification and in forest plantations, habitat generalists benefited. Furthermore, assemblages were impacted more by land use in tropical regions and landscapes containing a larger share of (semi)natural habitat compared with temperate regions and more converted landscapes. Given that mammal assemblage intactness is reduced also when diversification measures are in place, special attention should be directed to species that suffer from land use impacts. That said, our results suggest potential for reconciling land use and mammal conservation, provided that the diversification measures do not compromise yield.

Methodological Framework for Assessing Hydromorphological Conditions of Heavily Modified and Artificial River Water Bodies in Croatia

Water Framework Directive (WFD) guidance documents from 2019 provide a comprehensive review of methods and guidelines to improve the comparability of heavily modified water bodies (HMWBs) in the European Union. However, there is currently no common, single methodology for monitoring HMWBs and artificial water bodies (AWBs) or for determining maximum (MEP) and good ecological potential (GEP). This study presents the first assessment of hydromorphological conditions of HMWBs and AWBs in Croatia based on type-specific indicators. The typology of HMWBs and AWBs was based on distinct hydromorphological characteristics and modifications in order to be easily related to the uses of the water bodies. The classes of hydromorphological potential were graded from the theoretical MEP, which was determined by the score scale as the tolerated deviation from natural reference conditions, considering potential mitigation measures. The use of the water body and/or the effects on the wider environment were considered while determining MEP and choosing indicators included in monitoring and assessment. In the case of AWBs, the parameters dependent on natural reference conditions, which are non-existent, were omitted from the assessment. Only 27% of HMWBs and 2 out of 51 AWBs achieved good potential for all three hydromorphological elements. The most significant hydromorphological modifications include channelization, straightening, deepening and removal of riparian vegetation due to flood-protection management practices. In order to achieve the environmental objectives set out by the WFD, the Croatian water management system has to start implementing mitigation measures, especially related to natural flood management.

How degraded are the peatland and forest ecosystems in the Bieszczady Mountains (Central Europe)? An assessment using long‐term records

AbstractPeatland and forest ecosystems located in the Bieszczady Mts. (Carpathians, Central Europe) have been affected by human activity since the Neolithic, with this impact intensifying over time. We conducted long‐term studies to: (i) determine past peatland and forest development and current ecological state; (ii) assess the role of different factors that influenced ecosystem development over the last 3750 years; and (iii) determine natural reference conditions as a basis for the restoration of degraded mountain bogs and forests in the region. High‐resolution multi‐proxy palaeoecological analyses (plant macrofossils, pollen, testate amoebae, macro and microcharcoal, peat stoichiometry and stable isotopes), supported by radiocarbon dating, were performed on peat cores from an ombrotrophic peatland. Our study revealed that the peatland and forest ecosystems have been impacted by both climate change and human activity (fires, deforestation, and grazing) over the past 3750 years and that massive deforestation took place 400 years ago. Changes in forest composition led to the intensification in erosion between 3700–1500 cal. BP and over the past 350 years. Drainage resulted in hydrological disturbances but did neither stop the peat formation process nor decreased the abundance of species forming the natural peat plant communities indicative of oligotrophic conditions. However, hydrological disturbances shifted peat plant composition to dry‐adapted species (e.g. dwarf shrubs, Pinus sylvestris). Average water level depth fluctuated between ca. 10 and 25 cm over the last 3750 years; thus these are conditions that could be considered as hydrological reference for restoration measures. Our approach to identify natural reference conditions may be expanded to peatlands from other temperate mountain ranges.

Insight into the factors of mountain bog and forest development in the Schwarzwald Mts.: Implications for ecological restoration

Peatlands are a significant landscape component in temperate mountain ranges and serve multiple functions. However, many peatlands were damaged, altered, or drained over the past centuries, and knowledge about their development is needed for their protection and sustainable management. In our study, we analysed two peat cores from a bog site located in the Black Forest (Southwest Germany) using high-resolution multi-proxy palaeoecological analysis, including biological indicators (plant macrofossils, pollen, testate amoebae), macro-and micro-charcoal as well as geochemical analyses (peat stoichiometry and stable isotopes (δ13C, δ15N)) supported by radiocarbon dating. We tracked the development of the peatland and forest ecosystem to (i) determine their current ecological state, and to (ii) assess the role of different agents of change at the catchment scale on peatland development. The overall objective was to determine natural reference conditions as a basis for the restoration of degraded mountain bogs in the Black Forest Mountains and other temperate mountain ranges. Our results revealed that: i) the bog developed on mineral bedrock of slight slope through paludification around ca. 10,000 cal. BP; ii) the pristine plant populations dominated by Sphagnum fuscum occurring from 6200 cal. BP were replaced by Sphagnum medium/divinum and Eriophorum vaginatum since ca. 3300 cal. BP, most likely due to hydrological disturbances and possible dust deposition on the bog; iii) peat formation at the study site seems still active despite relatively deep water levels (ca. 22–26 cm below surface) and was active over the last 8000 years also when WTD varied between 12 and 26 cm; iv) the self-recovery of peat formation at this mountain bog is possible; v) the protection and restoration of mountain bog ecosystems should also consider land cover changes in the surrounding catchment, serving as further indicators or drivers of mountain bog development.

Reintroduction of native plants indicates the return of ecosystem services after iron mining at the Urucum Massif

AbstractTo reduce the net losses of biodiversity and ecosystem services caused by iron ore mining in Brazil, mineland rehabilitation using native plant species is necessary. However, systematic knowledge about which plant species are the best candidates for mineland rehabilitation is lacking. Therefore, iron mining companies working on the Urucum Massif reintroduce as many native herb and shrub species as possible to achieve the rehabilitation of savanna vegetation communities. To this end, seeds are collected from nearby native ecosystems, and seedlings are rescued from logged areas or produced in a local nursery. Monitoring is necessary to assess the persistence of the reinstated communities and their similarity to natural reference conditions. Ideally, monitoring efforts should compare the floristic composition of the rehabilitating sites with that of natural reference ecosystems. Here, we compared sites that had undergone two or three years of rehabilitation after iron ore mining on the Urucum Massif, MS, Brazil, with native reference sites. The species composition as well as structural, taxonomic, and phylogenetic diversity indices were compared between the reference and rehabilitating sites. Despite the differences in species composition between the rehabilitating and reference sites, we found more than 50 native species and partial recovery of the vegetation structure in the rehabilitating sites. Furthermore, we detected similar levels of animal‐dispersed plant species at rehabilitating and reference sites. These environmental indicators indicate that trial‐and‐error approaches are indeed able to establish considerable native species diversity during mineland rehabilitation. Furthermore, the partial recovery of the vegetation structure suggests the gradual return of soil functions in the long term, and the presence of zoochorous species is expected to attract seed‐dispersing animals that enable gene flow as well as the arrival of additional plant species. Nevertheless, the high cover values of alien exotic species, which are negatively correlated with the diversity of the reinstated communities, endanger the success of mineland rehabilitation in the Urucum Massif, and effective control methods for invasive populations are required. These efforts should be accompanied by enrichment plantings to maintain the diversity of native plant communities at the rehabilitation sites and ongoing environmental monitoring.

The assessment algorithm for sustainable development goals in the Hukiv, Dereluy, and Vyzhenka river basin systems of Chernivtsi oblast

The study deals with an integral assessment of hydromorphological and geoecological conditions of the Hukiv (flatland type of river), Dereluy (foothill type of river), and Vyzhenka (mountainous type of river) river basin systems (Figure 1). The indicators characterizing the river basin in the best way as a holistic system, the channel, floodplain, and watershed altogether, in natural reference conditions and in terms of human economic activity are addressed. The assessment hydromorphological test and geoecological monitoring of small rivers (SWOT-analysis) in accordance with the developed universal algorithm for hydromorphological assessment of small river basins for the sustainable development goals are generated and fulfilled. Interpretation maps for the sustainable development of the Hukiv, Dereluy and Vyzhenka rivers are created. The practical importance and relevance concerns the potential application of the proposed monitoring and the algorithm to solve methodological and applied problems related to the functioning of the systems “basin–river–human” and “basin–river–riverbed” in terms of modern human activity and needs; the need to modify consumer-type stereotypes for the use of natural resources, as well as to provide recommendations for enhancing the resource-efficient and sustainable activities in basin systems and small rivers.

Naturally changing reference conditions: Evidence of isostatic uplift being the main cause of changes in ecological status in a SW Norwegian fjord system

According to the European Water Framework Directive (WFD), restoration actions are needed if the present-day ecological quality status (EcoQS) is worse than good. However, less stringent environmental objectives may be allowed if the water body’s natural condition is such that it may be unfeasible or unreasonably expensive to achieve good conditions.In the Inner Skjolda- and Grindefjord, an isolated and shallow silled fjordsystem on the SW coast of Norway, the present EcoQS (based on benthic foraminifera and macroinvertebrates) is bad due to anoxic conditions in the bottom water. Paleoecological foraminiferal data in two dated sediment records were used to establish in situ reference conditions. The data revealed that the current bad EcoQS did not deviate from the natural reference condition which existed just prior to the onset of the industrial revolution. Further back in time, the record showed poor EcoQS and a strong dominance of the opportunistic foraminiferal species Stainforthia fusiformis, indicating unfavorable conditions for benthic foraminifera already >2000 years ago. The changing ecological status during the pre-industrial period was probably caused by the inner fjordsystem becoming gradually more isolated and stratified, and the bottom water more stagnant with decreasing oxygen concentrations, in response to isostatic uplift. Our study shows that reference conditions at a location may represent a natural succession of environmental changes i.e., the natural baseline does not have to represent only one environmental condition but may vary naturally over time. We therefore suggest that the conditions just prior to the onset of the industrial revolution should be used when defining reference conditions according to the WFD.

Groundwater fauna in an urban area – natural or affected?

Abstract. In Germany, 70 % of the drinking water demand is met by groundwater, for which the quality is the product of multiple physical–chemical and biological processes. As healthy groundwater ecosystems help to provide clean drinking water, it is necessary to assess their ecological conditions. This is particularly true for densely populated urban areas, where faunistic groundwater investigations are still scarce. The aim of this study is, therefore, to provide a first assessment of the groundwater fauna in an urban area. Thus, we examine the ecological status of an anthropogenically influenced aquifer by analysing fauna in 39 groundwater monitoring wells in the city of Karlsruhe (Germany). For classification, we apply the groundwater ecosystem status index (GESI), in which a threshold of more than 70 % of crustaceans and less than 20 % of oligochaetes serves as an indication for very good and good ecological conditions. Our study reveals that only 35 % of the wells in the residential, commercial and industrial areas and 50 % of wells in the forested area fulfil these criteria. However, the study did not find clear spatial patterns with respect to land use and other anthropogenic impacts, in particular with respect to groundwater temperature. Nevertheless, there are noticeable differences in the spatial distribution of species in combination with abiotic groundwater characteristics in groundwater of the different areas of the city, which indicate that a more comprehensive assessment is required to evaluate the groundwater ecological status in more detail. In particular, more indicators, such as groundwater temperature, indicator species, delineation of site-specific characteristics and natural reference conditions should be considered.

Representative boreal forest habitats in northern Europe, and a revised model for ecosystem management and biodiversity conservation

The natural range of variation of ecosystems provides reference conditions for sustainable management and biodiversity conservation. We review how the understanding of natural reference conditions of boreal forests in northern Europe has changed from earlier perceptions of even-aged dynamics driven by stand-replacing disturbances towards current understanding highlighting the role of non-stand-replacing disturbances and the resultant complex forest dynamics and structures. We show how earlier views and conceptual models of forest disturbance dynamics, including the influential ASIO model, provide estimates of reference conditions that are outside the natural range of variation. Based on a research synthesis, we present a revised forest reference model incorporating the observed complexity of ecosystem dynamics and the prevalence of old forests. Finally, we outline a management model and demonstrate its use in forest ecosystem management and show how regional conservation area needs can be estimated. We conclude that attaining favourable conservation status in northern Europe’s boreal forests requires increasing emphasis on ecosystem management and conservation for old forest characteristics.

Soil organic carbon stocks and sequestration rates of inland, freshwater wetlands: Sources of variability and uncertainty

Impacts of land use, specifically soil disturbance, are linked to reductions of soil organic carbon (SOC) stocks. Correspondingly, ecosystem restoration is promoted to sequester SOC to mitigate anthropogenic greenhouse gas emissions, which are exacerbating global climate change. Restored wetlands have relatively high potential to sequester carbon compared to other ecosystems, but SOC accumulation rates are variable, which leads to high uncertainty in sequestration rates. To assess soil properties and carbon sequestration rates of freshwater mineral soil wetlands, we analyzed an extensive database of SOC concentrations from the Prairie Pothole Region (549 wetlands over 160,000 km2), which is considered one of the largest wetland ecosystems in North America. We demonstrate that SOC of wetland catchments varies among inner, transition, toe slope, and upland landscape positions (LSPs), as well as among land uses and soil depth segments. Soil organic carbon concentrations were greatest in the inner portion of the catchment (66 Mg ha−1) and progressively decrease towards the upland LSP (43 Mg ha−1). We also conducted a regional extrapolation based on LSP- and land-use-specific SOC stocks, and estimated that wetland and upland areas of PPR wetland catchments contain 141 and 178 Tg of SOC in the upper 15 cm of the soil profile, respectively. Regressing SOC by restoration age (years restored) showed that sequestration rates, which differ by LSP and depth, ranged from 0.35 to 1.10 Mg ha−1 year−1. Using these SOC sequestration rates, along with data from natural and cropland reference sites, we estimated that it takes 20 to 64 years for SOC levels of restored wetlands to return to natural reference conditions, depending on LSP and depth segment. Accounting for LSP reduces uncertainty and should refine future assessments of the greenhouse gas mitigation potential from wetland restoration.

Effects of land use-induced vegetation and topography changes on soil chemistry in the Southern Alps (Ticino, Switzerland)

Effects of land use changes on chemical soil properties were studied in a southern alpine valley of Ticino, Switzerland by analysing three different land cover-topography units: (i) natural forested slopes (NFS); (ii) deforested, cultivated terraces (DCT), and (iii) reforested, abandoned terraces (RAT). Whereas NFS represents the natural reference state with negligible anthropogenic influence, DCT corresponds to intense agricultural utilization, and RAT refers to a post-cultural natural evolution after terrace cultivation. Land use-induced changes in vegetation cover and topography (i.e., terracing) had a clear influence on chemical soil properties. The presence or absence of the European chestnut (Castanea sativa Mill.), one of the main soil acidifying agents in the study area, clearly affected soil acidity, soil organic matter (SOM), and nutrient status. Compared to the vegetation change, terracing has a less obvious effect on soil chemistry. A greater effective rooting depth and a flat microtopography on terraces lead to a rapidly increased SOM accumulation due to better growing conditions for trees. Thus, the reforested, abandoned terraces develop peculiar soil chemistry conditions after 36 to 46 years of abandonment only.

Have some landscapes in the eastern Canadian boreal forest moved beyond their natural range of variability?

BackgroundIn the context of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec (Canada). Using contemporary and long-term fire cycles, each natural forest landscape is defined according to the variability of its structure and composition, and compared to the present-day landscape. This analysis was conducted to address the question of whether human activities have moved these ecosystems outside the range of natural landscape variability.MethodsThe study encompassed a forested area of 175 000 km2 divided into 14 landscapes. Using a framework that integrates fire cycles, age structure and forest dynamics, we characterized the forest composition and age structures that resulted from three historical fire cycles (110, 140, and 180 years) representative of the boreal forest of eastern Canada. The modeled natural landscapes were compared with present-day landscapes in regard to the proportion of old-growth forests (landscape level) and the proportion of late-successional forest stands (landscape level and potential vegetation type).ResultsFour landscapes (39%) remain within their natural range of variability. In contrast, nine landscapes (54%) show a large gap between natural and present-day landscapes. These nine are located in the southern portion of the study area, and are mainly associated with Abies-Betula vegetation where human activities have contributed to a strong increase in the proportion of Populus tremuloides stands (early-successional stages) and a decrease of old-growth forest stands (more than 100 years old). A single landscape (7%), substantially changed from its potential natural state, is a candidate for adaptive-based management.ConclusionComparison of corresponding natural (reference conditions) and present-day landscapes showed that ten landscapes reflecting an important shift in forest composition and age structure could be considered beyond the range of their natural variability. The description of a landscape’s natural variability at the scale of several millennia can be considered a moving benchmark that can be re-evaluated in the context of climate change. Focusing on regional landscape characteristics and long-term natural variability of vegetation and forest age structure represents a step forward in methodology for defining reference conditions and following shifts in landscape over time.

Using vegetation attributes to rapidly assess degradation of East African wetlands

Wetlands in East Africa harbor a large biodiversity and provide diverse ecosystem services. Also, wetlands are highly suitable for crop production due to generally fertile soils and water availability. As a result of rising demand for cropland that is driven by population growth, degradation of upland areas and changing food demand patterns, wetlands are increasingly used for agricultural production. Such land use changes can negatively affect biodiversity and the provision of ecosystem services, especially when formerly little-disturbed wetlands are converted into croplands. For evaluating wetlands and developing land use or conservation strategies, we require methods to assess disturbance and degradation of wetlands. For instance, many indices of biological integrity for wetlands using vegetation attributes have been developed especially in the USA, but to date, no comparable assessment schemes are available for East Africa. To develop such a scheme, we sampled four different wetland localities, covering both floodplain and inland valley wetlands in Kenya, Rwanda, Tanzania and Uganda. A total of 198 wetland plots were characterized regarding land use and evaluated in terms of geomorphology, hydrology, vegetation and water quality regarding their deviation from a theoretical natural reference state without human disturbances and given respective impact scores using the WET-Health approach. Additionally, nine variables characterizing vegetation attributes were recorded. The impact scores were rescaled from 0 to 1 and used as response variables in multiple linear regression models. The predictor variables were selected for each regression model out of the nine vegetation attributes in a stepwise process. The regression models for the different response variables differed strongly regarding their accuracy. The root mean square prediction error (RMSPE) ranged between 0.14 for the “vegetation disturbance” and 0.27 for the “hydrological modification” regression model. However, we conclude that vegetation attributes such as “absolute cover of perennial species” or “average height of vegetation” are generally useful to estimate anthropogenic impacts on East African wetlands as assessed with the WET-Health approach. The presented approach can hence be a pragmatic addition to the WET-Health approach as a cost-efficient and rapidly applicable method. Furthermore, it may also be useful for ex-post application to historic data and vegetation surveys.

Determining reference conditions of hemiboreal lakes in Latvia, NE Europe: a palaeolimnological approach

The current status of a lake can be evaluatedviamonitoring, but such data can only provide information about the last few decades to a century at best. In most cases, the natural state of a lake cannot be ascertained. This is even more challenging if the apparent anthropogenic effects on the environment over the last millennia are considered. We used data on fossil algae from five evenly distributed hemiboreal lakes in geographically different regions in Latvia, NE Europe to assess the amount of compositional change or turnover (i.e., the beta-diversity) in the algae datasets for the last 2000 years by using a Detrended Canonical Correspondence Analysis. Our results show that the algae turnover increases towards the present day with distinct shifts during times characterised by extensive and intensive agriculture establishment, and political and economic changes. Because the anthropogenic impact on the landscape and lakes before AD 1200 was relatively minor, we propose that algae composition at that time can be assumed to represent the natural reference conditions for most Latvian lakes.

WETLAND HYDROLOGICAL INTEGRITY ASSESSMENT WITH UNMANNED AERIAL SYSTEMS (UAS)

Abstract. A key component of the health status of a wetland ecosystem is the present hydrological integrity. The analysis of on-site activities that impact on the hydrology of a particular wetland was undertaken using an Unmanned Aerial System (UAS) in combination with field studies. The WET-Health methodology was followed for the hydrological assessment, where wetland health is a measure of the deviation of a wetland’s structure and function from its natural reference condition. The extent and nature of activities within the wetland such as impoundments, excavations and indicators of visible damage such as erosion gullies was determined through high resolution UAS mapping using a commercial off-the-shelf digital camera. Structure from Motion (SfM) computer vision techniques were used to derive ultra-high resolution point clouds, orthophotos, digital elevation models (DEMs) and digital terrain models (DTMs). Visual and statistical analyses of the point clouds and surface models were used to derive detailed information useful for enhanced hydrological health assessment of the wetland. The WET-Health hydrology module completed with the aid of the UAS products still indicated that the hydrology of the wetland is completely modified as indicated by the “F” Present Ecological State (PES) category and that the hydrological state of the wetland will deteriorate (change score). However a higher impact score was determined through the enhanced visualisation and completion of scale-appropriate measurements of hydrological features. In conclusion, the use of UAS can significantly enhance the assessment of surface hydrology of wetlands and thereby allow for more effective management, decision making and conservation of wetland ecosystems.

DETERMINATION OF THE PRESENT VEGETATION STATE OF A WETLAND WITH UAV RGB IMAGERY

Abstract. The compositional and structural characteristics of wetland vegetation play a vital role in the services that a wetland supplies. Apart from being important habitats, wetland vegetation also provide services such as flood attenuation and nutrient retention. South Africa is known to be a water scarce country. The protection and continuous monitoring of wetland ecosystems is therefore important. Factors such as site transformation and disturbance may completely change the vegetation of a wetland and the use of Unmanned Aerial Vehicle (UAV) imagery can play a valuable role in high-resolution monitoring and mapping. This study assessed if the use of UAV RGB imagery can enhance the determination of the present vegetation state of a wetland. The WET-Health level two (detailed on-site evaluation) methodology was followed for the vegetation assessment, where wetland health is a measure of the deviation of a wetland’s structure and function from its natural reference condition. The mapping of the disturbances classes was then undertaken using ultra-high resolution orthophotos, point clouds and digital surface models (DSM). The WET-Health vegetation module completed with the aid of the UAV products still indicates that the vegetation of the wetland is largely modified (“D” PES Category) and that the vegetation of the wetland will further deteriorate (change score). These results are the same as determined in the baseline study. However a higher impact (activities taking place within the wetland) score were determined. The assessment of various WET-Health vegetation indicators were significantly enhanced using the UAV imagery and derived products. The UAV products provided an accurate vantage point over the wetland and surroundings, and assisted to easily refine the assessment of the disturbance classes and disturbance units.

WETLAND VEGETATION INTEGRITY ASSESSMENT WITH LOW ALTITUDE MULTISPECTRAL UAV IMAGERY

Abstract. The use of multispectral sensors on Unmanned Aerial Vehicles (UAVs) was until recently too heavy and bulky although this changed in recent times and they are now commercially available. The focus on the usage of these sensors is mostly directed towards the agricultural sector where the focus is on precision farming. Applications of these sensors for mapping of wetland ecosystems are rare. Here, we evaluate the performance of low altitude multispectral UAV imagery to determine the state of wetland vegetation in a localised spatial area. Specifically, NDVI derived from multispectral UAV imagery was used to inform the determination of the integrity of the wetland vegetation. Furthermore, we tested different software applications for the processing of the imagery. The advantages and disadvantages we experienced of these applications are also shortly presented in this paper. A JAG-M fixed-wing imaging system equipped with a MicaScene RedEdge multispectral camera were utilised for the survey. A single surveying campaign was undertaken in early autumn of a 17 ha study area at the Kameelzynkraal farm, Gauteng Province, South Africa. Structure-from-motion photogrammetry software was used to reconstruct the camera position’s and terrain features to derive a high resolution orthoretified mosaic. MicaSense Atlas cloud-based data platform, Pix4D and PhotoScan were utilised for the processing. The WET-Health level one methodology was followed for the vegetation assessment, where wetland health is a measure of the deviation of a wetland’s structure and function from its natural reference condition. An on-site evaluation of the vegetation integrity was first completed. Disturbance classes were then mapped using the high resolution multispectral orthoimages and NDVI. The WET-Health vegetation module completed with the aid of the multispectral UAV products indicated that the vegetation of the wetland is largely modified (“D” PES Category) and that the condition is expected to deteriorate (change score) in the future. However a lower impact score were determined utilising the multispectral UAV imagery and NDVI. The result is a more accurate estimation of the impacts in the wetland.

Assessing the ecological quality of the Port Blair coast (South Andaman, India) using different suites of benthic biotic indices

Six benthic biotic indices (Shannon–WienerH′log2, W-statistics, BOPA, BENTIX, AMBI and M-AMBI), based on different ecological principles, were applied to assess the health of variously disturbed tropical intertidal habitats of the Port Blair coastline. A total of 243 replicate samples were collected during the dry period (January, February and March) of 2014–2016. Temperature, salinity, dissolved oxygen, sediment pH, total organic matter content and texture were analysed. A high mean abundance of opportunistic species (Orbiniasp. 748,Capitella singularis237 andArmandiasp. 114 ind. m−2) was observed at Phoenix Bay, a gradual decline in diversity at Junglighat and a comparatively high diversity and moderate biomass at Wandoor, reflecting a human pressure gradient. Results showed an annual decline of benthic quality from 2014 to 2016 (good to moderate). Overall BOPA failed to distinguish the magnitude of disturbances, while the rest of the indices classified the benthic quality from undisturbed/high (WD), slightly disturbed/good (JG), to moderately disturbed/moderate to poor (PB). The subjective analysis demonstrated that the urban centres corresponded to disturbed benthic communities of dominant first and second order opportunistic species, while sensitive (EGI) and indifferent (EGII) were associated with the least disturbed or undisturbed site. The study successfully demonstrated the performance of temperate indices in intertidal habitats against the mild organic enrichment. However, for an effective assessment, setting natural reference conditions and sampling in stable dry periods (strong seasonality in tropics) is desirable. In order to test the performance of biotic indices, a long-term monitoring approach of taking abiotic and biotic descriptors into account is recommended.

Coupled use of sediment phosphorus speciation and pigment composition to infer phytoplankton phenology over 700 years in a deep oligotrophic lake

Restoration and management of lake ecosystems require an understanding of natural variability in primary productivity and the factors that drive change. To understand long-term changes in, and relationships amongst phosphorus species and phytoplankton groups, a sediment core was retrieved from Lake Okataina in the central North Island of New Zealand. The core was dated to include a period of approximately 700 years, from pre-human settlement to its current state, close to natural reference conditions. Pigments representing different planktonic groups were measured vertically through the core at 1 cm intervals, as well as phosphorus fractions associated with apatite and CaCO3, Fe and Mn (oxy) hydroxides, Al (oxy) hydroxides and labile phosphorus. Highly significant correlations were established amongst the algal groups and the phosphorus species. Diatoms were strongly correlated with phosphorus fractions associated with permanent burial, while cyanobacteria and green algae were correlated with potentially bioavailable phosphorus. Green algae, cyanobacteria and cryptophytes co-dominated when diatom populations were reduced, and vice versa. Using multiple linear regression, phosphorus fractions could be used to hindcast historical variations in the composition of algal communities (as inferred from pigments), with the exception of alloxanthin (representative of cryptophytes). Our approach provides a technique for a relatively rapid assessment of long-term changes in the major phytoplankton groups in lakes and may be used to infer natural variability in the reference state as well as partitioning the extent of alteration of phytoplankton community composition between human and natural disturbances.