How a reservoir modulates downstream water quality under declining upstream loading and progressing climate change

Area of Science:

• Environmental Science
• Hydrology
• Ecology

Background:

• Reservoirs play a crucial role in regulating water flow and nutrient transport within catchments.
• Climate change poses a significant threat to the effective functioning of reservoirs in managing water quality.

Purpose of the Study:

• To investigate the intricate relationship between climate variables and nutrient pollution dynamics in the Möhne reservoir catchment.
• To understand how reservoirs influence downstream nutrient levels under changing climatic conditions.

Main Methods:

• Analysis of a multi-decadal time series dataset from the Möhne reservoir catchment.
• Comparison of upstream and downstream nutrient concentrations (total nitrogen and total phosphorus).
• Assessment of trends in nutrient levels in relation to climate data, streamflow, and wastewater management improvements.

Main Results:

• The reservoir demonstrated a general nutrient-trapping capacity, with higher upstream than downstream concentrations.
• Upstream total nitrogen (TN) and total phosphorus (TP) showed declining trends due to better wastewater management and reduced runoff.
• Downstream TN decreased, while TP slightly increased, attributed to reservoir warming, reduced dissolved oxygen, promoting denitrification and internal phosphorus loading.

Conclusions:

• Contrasting downstream TN and TP trends alter nutrient stoichiometry, potentially disrupting riverine ecosystem biogeochemical processes.
• Warming climates may cause reservoirs to differentially affect nitrogen and phosphorus, leading to ecological discontinuities.
• Adaptable nutrient management strategies are essential for reservoir catchments to mitigate climate change impacts.