| Abstrakt: |
Abell JM, Özkundakci D, Mcbride CG, Allan MG. 2024. Estimating nutrient load targets for lakes at a regional scale. Lake Reserv Manag. 40:354–372. Estimating target nutrient loads to achieve desired lake water quality is challenging due to complex relationships between nutrient loading and in-lake concentrations. We analyzed lake water quality data and existing catchment model output to evaluate empirical nutrient loading models for 21 lakes in the Waikato region of New Zealand that had varying total nitrogen (TN) and total phosphorus (TP) concentrations. The optimum model, which included water residence time (τw) and inflow concentrations as predictors, was used to estimate target TN and TP loads necessary to meet target in-lake nutrient concentrations. Uncertainty in load estimates was estimated using bootstrapping. Results highlighted the substantial challenge facing lake managers: for lakes with in-lake concentrations exceeding targets, current TN loads were 21 times greater than target loads on average (standard deviation = 39 times), whereas current TP loads were ∼3 times greater than target loads on average (standard deviation = 3.1 times). To inform management more broadly, models were used to estimate target inflow concentrations for hypothetical lake restoration scenarios comprising varying target in-lake concentrations and τw. Scenario analysis quantified the major role of τw, with lower target inflow concentrations (i.e., greater load reductions) required to achieve in-lake nutrient targets in lakes with lower τw. For the scenarios analyzed, results showed the lakes are phosphorus sinks, but may switch from being a sink to a source of nitrogen as τw decreases. The approach used provides a reference for other jurisdictions faced with managing lakes with limited datasets and the results can inform lake management policy for similar lakes. [ABSTRACT FROM AUTHOR] |
