Rising temperatures and altering precipitation because of climate change is affecting aquatic reservoirs across the US, says a study
Climate change, along with ageing, is threatening reservoir aquatic habitats, a study found. While ageing affects in-lake habitats directly, climate change affects both in-lake and of-lake conditions. The study found that climate change is expected to accelerate and, in some instances, possibly decelerate ageing. These events are projected to transform reservoir aquatic habitats in various and often unpredictable ways.
(Ageing can be indexed as functional age, an index that signals the position of a reservoir along its lifespan relying on in-lake descriptors of aquatic habitat. Ageing is linked to sedimentation, eutrophication, homogenisation of substrates and shorelines, and changes in water quality that shift aquatic biotic assemblages mostly towards degraded states that do not adequately meet social and ecological standards.)
The researchers developed semi-quantitative predictions about the effect of climate change on reservoir functional age in the USA, using existing habitat datasets and climate projections.
The analysis predicted that warming and shifts in precipitation would affect functional ageing patterns differently. In response to warming, functional ageing was projected to increase latitudinally from south to north. In response to total annual precipitation, functional age also showed a latitudinal increase, but in addition showed a longitudinal pattern where functional ageing was least in mid-sections of the country and increased in the east and the west.
The study revealed that reservoir functional ageing combined with climate change has the potential to change aquatic habitats, biotic assemblages, and fisheries in reservoirs by influencing habitat quality and quantity, and by altering species associations and interactions.
Ecological and biological impacts
The study found that projected climate change can impact the reservoir catchment, water storage, water quality, and ecological characteristics. Catchment impacts may result from shifts in extent of runoff, and associated transport of sediment and nutrients. Water storage impacts could include changes in water residence time and water levels. Consequences on water quality can arise from shifts in stratification, accelerated eutrophication, and increased incidence of anoxia and chemical characteristics associated with increased temperature and reduced oxygen, added the study.
The major changes in biological characteristics which can influence aquatic habitat included harmful plankton blooms, changes in microbial activity, shifts in phytoplankton and macrophyte assemblages, and proliferation of exotic species. In southern latitudes, noted the report, reductions in the frequency and intensity of cold winter temperatures can allow tropical and subtropical species to move northward and replace temperate species. Where climatic thresholds are crossed, certain ecosystems and landscapes may be transformed, the report warned.
The study found that increased precipitation and soil moisture in a warmer climate also can cause increased loss of soil carbon that may in due course reach reservoirs and promote eutrophication including reduced transparency and accompanying impacts on food webs. Transitions from extremes of drought to foods increase nitrogen inputs into reservoirs and can intensify harmful algal blooms. Together, these changes are likely to influence aquatic habitats in loosely predictable ways.
The effects, noted the study, may differ greatly across geographical regions given the differences in predicted climate patterns, and even within regions given the high diversity of reservoirs with respect to elevation, surface area, depth, inflow volume, water residence time, sediment and nutrient influx, operation, and biotic assemblage composition.
However, the projections were tentative because of the uncertain nature of reservoir ageing and climate change sciences. Adaptation involves developing strategies to increase the capacity of reservoir ecosystems to absorb disturbances and retain the ability to self-regulate despite ageing. The study mentioned that a resilient reservoir may be better positioned to serve its purposes under the predictable and the unpredictable conditions generated by transition caused by a mix of ageing and climate change.