Spatiotemporal hierarchical models to assess the influence of climate, land use, and hydrology on water quality in Itaipu Reservoir, Brazil

The eutrophication process in reservoirs differs from that observed in natural lakes, mainly because tributary arms enhance the reservoir’s connectivity with their watersheds. This study evaluated how climate, land use, and hydrology influence phosphorus, nitrogen, chlorophyll-a, algal bloom area, and macrophyte cover in a reservoir through spatiotemporal hierarchical linear mixed-effects models. To assess this, we used limnological, meteorological, remote sensing, and hydrological data in three tributary arms monitored by the Itaipu Hydroelectric Power Plant program covering the period from 1985 to 2021. The models were used to assess the relationships between environmental drivers and water quality indicators. Our findings suggest that the reservoir water level and temperature are important drivers of eutrophication, particularly for algal bloom area and macrophyte cover. Land use processes within the watersheds were associated with changes in water quality of the reservoir’s tributary arms. For example, the urban land use significantly increased phosphorus levels, macrophyte cover, and algal bloom area, while temporary crops increased chlorophyll-a concentrations. Pastureland and/or cattle production were associated with increases in all water quality indicators. These findings highlight the critical role of hydrological management and land use planning in mitigating eutrophication in large tropical reservoirs.