Increasing Hydroperiod in a Karst-depression Wetland Based on 165 Years of Simulated Daily Water Levels

The hydrology of seasonally inundated depression wetlands can be highly sensitive to climatic fluctuations. Hydroperiod—the number of days per year that a wetland is inundated—is often of primary ecological importance in these systems and can vary interannually depending on climate conditions. In this study we re-examined an existing hydrologic model to simulate daily water levels in Sinking Pond, a 35-hectare seasonally inundated karst-depression wetland in Tennessee, USA. We recalibrated the model using 22 years of climate and water-level observations and used the recalibrated model to reconstruct (hindcast) daily water levels over a 165-year period from 1855 to 2019. A trend analysis of the climatic data and reconstructed water levels over the hindcasting period indicated substantial increases in pond hydroperiod over time, apparently related to increasing regional precipitation. Wetland hydroperiod increased on average by 5.9 days per decade between 1920 and 2019, with a breakpoint around the year 1970. Hydroperiod changes of this magnitude may have profound consequences for wetland ecology, such as a transition from a forested wetland to a mostly open-water pond at the Sinking Pond site. More broadly, this study illustrates the needs for robust hydrologic models of depression wetlands and for consideration of model transferability in time (i.e., hindcasting and forecasting) under non-stationary hydroclimatic conditions. As climate change is expected to influence water cycles, hydrologic processes, and wetland ecohydrology in the coming decades, hydrologic model projections may become increasingly important to detect, anticipate, and potentially mitigate ecological impacts in depression wetland ecosystems.

Evaluation of changes in ecological conditions of wetlands in the Teniz-Korgalzhin depression (Kazakhstan)

The article presents the results of a study of the long-term dynamics of the state of ecosystems of the Teniz-Korgalzhyn depression, carried out using data from the Earth remote sensing (ERS). Based on the analysis of space images, the formation factors of modern environmental conditions are established. In the study area, such factors are positional and barrier factors, as well as the confinement of individual surface sections to different-height layers of the Earth's surface. An analysis of the Landsat series of space images taken at different time, made it possible to establish spatial differences in the intensity of phytomass accumulation in areas located in different landscape locations. The spatio-temporal variability of the ecological conditions of the Teniz-Korgalzhin depression wetlands is accompanied by a change in the amount of food supply and the number of living organisms. Monitoring of these changes on the basis of Earth remote sensing data will allow to prove measures to preserve the biodiversity of the Teniz-Korgalzhin depression wetlands timely.

Basin-scale impacts of hydropower development on the Mompós Depression wetlands, Colombia

A number of large hydropower dams are currently under development or in an advanced stage of planning in the Magdalena River basin, Colombia, spelling uncertainty for the Mompós Depression wetlands, one of the largest wetland systems in South America at 3400 km2. Annual large-scale inundation of floodplains and their associated wetlands regulates water, nutrient, and sediment cycles, which in turn sustain a wealth of ecological processes and ecosystem services, including critical food supplies. In this study, we implemented an integrated approach focused on key attributes of ecologically functional floodplains: (1) hydrologic connectivity between the river and the floodplain, and between upstream and downstream sections; (2) hydrologic variability patterns and their links to local and regional processes; and (3) the spatial scale required to sustain floodplain-associated processes and benefits, like migratory fish biodiversity. The implemented framework provides an explicit quantification of the nonlinear or direct response relationship of those considerations with hydropower development. The proposed framework was used to develop a comparative analysis of the potential effects of the hydropower expansion necessary to meet projected 2050 electricity requirements. As part of this study, we developed an enhancement of the Water Evaluation and Planning system (WEAP) that allows resolution of the floodplains water balance at a medium scale (∼ 1000 to 10 000 km2) and evaluation of the potential impacts of upstream water management practices. In the case of the Mompós Depression wetlands, our results indicate that the potential additional impacts of new hydropower infrastructure with respect to baseline conditions can range up to one order of magnitude between scenarios that are comparable in terms of energy capacity. Fragmentation of connectivity corridors between lowland floodplains and upstream spawning habitats and reduction of sediment loads show the greatest impacts, with potential reductions of up to 97.6 and 80 %, respectively, from pre-dam conditions. In some development scenarios, the amount of water regulated and withheld by upstream infrastructure is of similar magnitude to existing fluxes involved in the episodic inundation of the floodplain during dry years and, thus, can also induce substantial changes in floodplain seasonal dynamics of average-to-dry years in some areas of the Mompós Depression.

Large-scale impacts of hydropower development on the Mompós Depression wetlands, Colombia

A number of large hydropower dams are currently under development or in an advanced stage of planning in the Magdalena River basin, Colombia, spelling uncertainty for the Mompós Depression wetlands, one of the largest wetland systems in South America. Annual large-scale inundation of floodplains and associated wetlands regulates water-, nutrient-, and sediment cycles, which in turn sustain a wealth of ecological processes and ecosystem services, including critical food supplies. In this study, we present a comparative analysis of the potential effects of hydropower expansion to meet projected electricity requirements by 2050, in terms of 1) basin-level implications of cumulative changes in streamflow regime, sediment trapping, and loss of river connectivity, and 2) the impact of upstream regulation on the hydrologic dynamics of the Mompós Depression wetlands at a monthly to decadal scale. To this end, we developed an enhancement of the Water Evaluation and Planning system (WEAP) that allows resolution of the Mompós Depression floodplains water balance at a medium scale (~1000 to 10 000 km2) and evaluation of the potential impacts of upstream water management practices. Our results indicate that potential additional impacts of new hydropower infrastructure with respect to baseline conditions can range up to one order of magnitude between scenarios that are comparable in terms of energy capacity. Fragmentation of connectivity corridors between lowland floodplains and upstream spawning habitats and reduction of sediment loads show the greatest impacts, with potential reductions of up to 97.6 and 80 %, respectively, from pre-dam conditions. In some development scenarios, the amount of water regulated and withheld by upstream infrastructure is of similar magnitude to existing fluxes involved in the episodic inundation of the floodplain during dry periods and, thus, can also induce substantial changes in floodplain seasonal dynamics of average-to-dry years in some areas of the Mompós Depression.

Assessment of the physicochemical characteristics of surface waterbodies in a region earmarked for shale gas exploration (Eastern Cape Karoo, South Africa)

The proposed drilling for shale gas resources in the Eastern Cape Karoo region of South Africa has triggered much debate over the potential effects of hydraulic fracturing on water resources. Herein we present results on some limnological aspects of surface waterbodies in this water-scarce region before shale gas exploration. Thirty-three waterbodies (nine dams, 13 depression wetlands and 11 rivers) were sampled in November 2014 and April 2015. Principal component analysis revealed that depression wetlands and rivers had distinct physicochemical signatures, whereas dams were highly variable in their physicochemical attributes and exhibited characteristics similar to those of either rivers or depression wetlands. Non-parametric multivariate regressions and permutational multivariate analysis of variance (MANOVA) indicated that landscape variables such as underlying geology, altitude and land use poorly explained the physicochemical characteristics of the sampled waterbodies. Waterbody type was the only factor that explained a significant amount of the variation in physicochemistry during both sampling events. These data need to be supplemented by water quality information from additional sites and over longer time periods, as well as supporting data relating to other aspects, such as algae and invertebrates, before they can be used as a baseline for the long-term monitoring of freshwater ecosystems in the region.