1. Contrasting Impacts of Agricultural Intensification and Urbanization on Lake Phosphorus Cycling and Implications for Managing Eutrophication.
- Author
-
Slowinski, Stephanie, Radosavljevic, Jovana, Graham, Alyssa, Ippolito, Isabella, Thomas, Kathryn, Rezanezhad, Fereidoun, Shafii, Mahyar, Parsons, Chris T., Basu, Nandita B., Wiklund, Johan, Hall, Roland I., and Van Cappellen, Philippe
- Subjects
EUTROPHICATION ,AGRICULTURAL intensification ,URBAN runoff management ,WATER quality ,URBAN watersheds ,BIOLOGICAL productivity ,CYCLING competitions ,FREIGHT trucking - Abstract
Sediment core and water quality data, together with historical information on land use/land cover (LULC), were used to reconstruct changes in phosphorus (P) loading and cycling in Lake Wilcox, Ontario, Canada, since the early 1920s. After first being cleared for farming, the originally forested watershed subsequently underwent urbanization. The large increase in P loading accompanying agricultural intensification after World War II caused the eutrophication of the lake. However, improved soil conservation since the 1980s and urban stormwater management since the 1990s have brought watershed P loading and sediment accumulation down to levels comparable to the early 1900s. Yet, the lake continues to exhibit eutrophication‐like symptoms, especially the intensification of hypoxia in the hypolimnion. Post‐2000 water quality data indicate that the latter is not driven by external P loading from the watershed, but rather by rapid salinization that strengthens the lake's summer stratification and enhances internal P loading. Salinization is caused by the increasing application of deicing agents in the expanding urban area. Curbing salt inputs will therefore be essential to restore the lake. Overall, our results provide new insights into the shifts in lake biogeochemistry associated with LULC changes and the implementation of best management practices. The approaches and findings of our case study have broad applicability for the large number of freshwater ecosystems worldwide that are experiencing salinization. Plain Language Summary: The impacts of a century of land use changes on a receiving lake were analyzed, from the early land clearing for farming to the recent rapid urban growth. We focused on the loading of the nutrient element phosphorus (P) to the lake and the resulting changes in water quality and biological productivity. The lake experienced the highest P loading during the period of intensive farming following World War II, which stimulated algal growth and the depletion of dissolved oxygen in the lake's deeper part. Since the 1980s, soil conservation measures have helped in reducing P loading and reversing water quality deterioration. From the early 1990s till today, as the urban area expanded, the lake saw its P loading drop to its lowest level because of the retention of P in urban stormwater ponds. Nonetheless, the lake still suffers from low oxygen concentrations. This is explained by the rising application of road salt in the urban areas of the watershed. The saltier runoff makes it more difficult for the lake to mix and reduces the amount of oxygen in the deeper waters. Thus, controlling salt, rather than P, loading to the lake will be needed to restore the lake. Key Points: Sediment core data link historical changes in land use/land cover to lake phosphorus loading, trophic state, and bottom water oxygenationExternal phosphorus loading and sediment burial peaked during agricultural intensification and dropped with urbanization of the watershedAgricultural soil conservation practices and urban stormwater ponds are very effective at lowering watershed phosphorus exports [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF