Temporal changes to spatially stratified waterbird communities of the Coorong, South Australia: implications for the management of heterogenous wetlands

Extreme eutrophication and salinisation in the Coorong estuarine-lagoon ecosystem of Australia's largest river basin (Murray-Darling)

Estuaries in rainfall poor regions are highly susceptible to climatic and hydrological changes. The Coorong, a Ramsar-listed estuarine-coastal lagoon at the end of the Murray-Darling Basin (Australia), has experienced declining ecological health over recent decades. Twenty years of environmental data were analysed to assess patterns and drivers of water quality changes. Large areas of the Coorong are now persistently hyper-saline (salinity >80 psu) and hypereutrophic (total nitrogen, TN > 4 mg L^-1, total phosphorus, TP > 0.2 mg L^-1, chlorophyll a > 50 μg L^-1) which coincided with reduced flushing due to diminished freshwater inflows and increasing evapo-concentration. Sediment quality also was related to flushing, with higher concentrations of organic carbon, TN, TP and sulfides as salinity increased. While total nutrient levels are very high, dissolved inorganic nutrients are generally low. Increased lagoonal flushing would be beneficial to reduce the hypersalinisation and hypereutrophication and improve ecosystem health.

Resurrecting seasonal dynamics in waterbirds after wetland restoration: before-after monitoring highlights the role of a single dominant species

We compared a set of uni-varied diversity metrics of a guild of water-related birds (hereafter 'waterbirds') before and after a wetland restoration carried out on uncultivated (reclaimed) lands. Over a period of five years, we observed a restart of seasonal waterbirds dynamics after wetland restoration by flooding of abandoned croplands, with a significant increase in all metrics of diversity, more evident in autumn-winter periods. Seasonal thresholds were evident before (2017-2018) and after (2018-2019) the flooding. These dynamics appeared irregular, probably for a different inter-annual suitability of the flooded meadows due to local ecological factors (e.g., change in meteorological regime and in rush-bed vegetation cover). Rarefaction curves, both for richness and diversity, showed how the waterbird community moved towards a greater complexity. Flooded meadow restoration, particularly favoured wintering species in Mediterranean sites, which explained the strong fluctuations in total abundance. At the species level, Northern Lapwing (Vanellus vanellus), absent before restoration, was the most abundant species after flooding, using flooded meadows with its gregarious behaviour. This 'crowding' may be explained also for a lack of similar habitats in the surrounding. Other dominant species (Anas platyrhynchos, Ardea cinerea, Egretta garzetta) showed a significant increase after restoration. Standardized before-after monitoring on medium term time periods seem suitable to evidence inter-annual season dynamics in diversity metrics of waterbird assemblages.

Heavy metal exposure to a migratory waterfowl, Northern Pintail (Anas acuta), in two peri-urban wetlands

In this study, the heavy metal exposure risk model was employed to assess the exposure risk to a predominantly herbivore waterfowl, Northern Pintail, wintering in two wetland habitats in the Purulia district of West Bengal, located on overlapping Central Asian Flyway (CAF) and East Asian-Australasian Flyway (EAAF). Both wetlands were important staging and roosting grounds for migratory waterfowl for ages. The exposure model was used to quantify the risk of exposure to metals through oral ingestion. Exposure doses of Cu, Zn, Pb, and Cr through food plants ingestion and food-associated sediment consumption pathways were two potent sources of heavy metal exposure in the waterfowl under study. Exposure through water intake was ignored as metals were either of negligible concentrations or below the detection limit in water samples. Heavy metal concentrations showed significant positive correlations between bottom sediment and plant at both sites. At Purulia Sahebbandh (Site 1), the total exposure dose of all four metals was much higher than their conforming tolerable daily intake (TDI), and thereby, the metals might pose threats to the migratory wintering herbivorous waterfowl populations. However, in Adra Sahebbandh (Site 2), total exposure doses of Pb, Zn and Cu were much below their corresponding TDI. The Hazard Quotient (HQ) of Cr was highest followed by nonessential toxic Pb and these two elements could be considered as priority pollutants at Site 1. Prioritize threats were decreased in the following sequence: Cr > Pb > Cu > Zn at Site 1 and Cr > Zn > Pb > Cu at Site 2. Hazard Index was found to be >5 at Site 1 and for much higher metal loads a significant correlation between metal concentrations in plants, bottom sediment and exposure doses were also recorded. Therefore, the peri-urban Purulia Sahebbandh wetland could immediately be considered for risk control and demanded holistic management of important waterfowl habitats.

Hydro-Saline Dynamics of a Shallow Mediterranean Coastal Lagoon: Complementary Information from Short and Long Term Monitoring

The Vaccarès Lagoon System, located in the central part of the Rhône Delta (France), is a complex shallow coastal lagoon, exposed to a typical Mediterranean climate and a specific hydrological regime affected by man-controlled exchanges with the sea and agricultural drainage channels. In this article, we report the results obtained by a series of monitoring programs, with different spatial and temporal resolutions. Long-term datasets from 1999 to 2019 with data collected on a monthly basis and a high spatial resolution highlighted the significant spatial heterogeneity in salinity regimes, and helped to determine the long-term evolution of the total mass of dissolved salt. High-frequency surveys allowed to characterize the water levels and salinity dynamics seasonal response to (i) the exchanges with the Mediterranean Sea, (ii) the exchanges with agricultural drainage channels, and (iii) the rain and evaporation. In addition, wind effects on salinity variations are also explored. This work shows how different spatial and temporal monitoring strategies provide complementary information on the dynamic of such a complex system. Results will be useful and provide insight for the management of similar lagoon systems, accommodating for both human activities and ecological stakes in the context of global change.

Continental impacts of water development on waterbirds, contrasting two Australian river basins: Global implications for sustainable water use

The world's freshwater biotas are declining in diversity, range and abundance, more than in other realms, with human appropriation of water. Despite considerable data on the distribution of dams and their hydrological effects on river systems, there are few expansive and long analyses of impacts on freshwater biota. We investigated trends in waterbird communities over 32 years, (1983-2014), at three spatial scales in two similarly sized large river basins, with contrasting levels of water resource development, representing almost a third (29%) of Australia: the Murray-Darling Basin and the Lake Eyre Basin. The Murray-Darling Basin is Australia's most developed river basin (240 dams storing 29,893 GL) while the Lake Eyre Basin is one of the less developed basins (1 dam storing 14 GL). We compared the long-term responses of waterbird communities in the two river basins at river basin, catchment and major wetland scales. Waterbird abundances were strongly related to river flows and rainfall. For the developed Murray-Darling Basin, we identified significant long-term declines in total abundances, functional response groups (e.g., piscivores) and individual species of waterbird (n = 50), associated with reductions in cumulative annual flow. These trends indicated ecosystem level changes. Contrastingly, we found no evidence of waterbird declines in the undeveloped Lake Eyre Basin. We also modelled the effects of the Australian Government buying up water rights and returning these to the riverine environment, at a substantial cost (>3.1 AUD billion) which were projected to partly (18% improvement) restore waterbird abundances, but projected climate change effects could reduce these benefits considerably to only a 1% or 4% improvement, with respective annual recovery of environmental flows of 2,800 GL or 3,200 GL. Our unique large temporal and spatial scale analyses demonstrated severe long-term ecological impact of water resource development on prominent freshwater animals, with implications for global management of water resources.

Changes in distribution of waterbirds following prolonged drought reflect habitat availability in coastal and inland regions

Provision of suitable habitat for waterbirds is a major challenge for environmental managers in arid and semiarid regions with high spatial and temporal variability in rainfall. It is understood in broad terms that to survive waterbirds must move according to phases of wet–dry cycles, with coastal habitats providing drought refugia and inland wetlands used during the wet phase. However, both inland and coastal wetlands are subject to major anthropogenic pressures, and the various species of waterbird may have particular habitat requirements and respond individualistically to spatiotemporal variations in resource distribution. A better understanding of the relationships between occurrence of waterbirds and habitat condition under changing climatic conditions and anthropogenic pressures will help clarify patterns of habitat use and the targeting of investments in conservation. We provide the first predictive models of habitat availability between wet and dry phases for six widely distributed waterbird species at a large spatial scale. We first test the broad hypothesis that waterbirds are largely confined to coastal regions during a dry phase. We then examine the contrasting results among the six species, which support other hypotheses erected on the basis of their ecological characteristics. There were large increases in area of suitable habitat in inland regions in the wet year compared with the dry year for all species, ranging from 4.14% for Australian White Ibis to 31.73% for Eurasian Coot. With over half of the suitable habitat for three of the six species was located in coastal zones during drought, our study highlights the need to identify and conserve coastal drought refuges. Monitoring of changes in extent and condition of wetlands, combined with distribution modeling of waterbirds, will help support improvements in the conservation and management of waterbirds into the future.

Drought increases the impact of introduced European foxes on breeding Australian pelicans

Context Introduced mammalian predators have been responsible for population declines in native prey species around the world. Many conservation programs rely on control or eradication of introduced mammalian predators, but the impact of environmental variation on the efficacy of this approach is rarely documented. Aims The present paper describes (1) the impact of introduced European foxes (Vulpes vulpes) on breeding Australian pelicans (Pelecanus conspicillatus) in South Australia and (2) the responses of both species to a fox-eradication program using a before-after-impact framework. Methods The impact of foxes on breeding Australian pelicans was studied on a near-shore island. An index of fox abundance and direct measurements of breeding pelicans and mortality of pelican eggs and young were compared before foxes were established on the island, while foxes were resident and during a fox-eradication program. A path analysis was used to explore the causal relationships between fox abundance and other potential covariates (e.g. rainfall) on breeding pelicans. Key results Before foxes were established on the island, the number of breeding pelicans grew and egg mortality was low. While foxes were resident, the number of breeding pelicans fell and egg mortality rose. This was followed by an increase in the number of breeding pelicans and a decrease in egg mortality during a fox-eradication program. While foxes had a clear impact on egg mortality, a period of low rainfall also occurred while foxes were resident. The path analysis showed an interaction among rainfall, size of the pelican breeding population and the impact of foxes. In drought years, fewer pelicans bred and foxes were a major cause of nest abandonment when they entered pelican breeding colonies to prey on eggs. Conclusions These results confirmed that foxes can be an important predator of ground-nesting, colonial waterbirds, and showed that the impact of foxes may be higher in drought years when prey populations are low. Implications The present study suggests that an increase in the incidence of droughts as a result of climate change may increase the impact of introduced predators on drought-sensitive waterbirds and raises the possibility of focussing predator-control efforts during droughts, as periods of particular risk to colony-breeding waterbirds.