Nutrient loading to lakes depends on both the availability of nutrients in a watershed and their potential for movement to a lake. Many studies have demonstrated that variation in watershed land use can translate to differences in lake water quality by affecting nutrient availability. There have been few attempts, however, to understand how loading to surface waters is affected by land use when there are differences in watershed transport capacity. We compared the relationship between land use/cover and lake nutrients in lakes draining watersheds that exhibited high and low transport capacity using a 5 year (2001-2005) dataset describing the chemistry of 101 lakes and reservoirs in a region of intensive agriculture. We measured watershed transport capacity by compositing the hydrologic, geologic, and topographic variables correlated with interannual variability in lake total nitrogen (TN) or phosphorus (TP) because the hydrologic permeability of watersheds amplifies downstream responses to rainfall events. Factors describing watershed transport capacity differed for TN and TP, consistent with differences in nutrient mobility and biogeochemistry. Partial least squares regression revealed that watershed transport capacity influenced the nature of the association between land use/cover and lake chemistry. In watersheds with low transport capacity, in-lake processes and near-shore land use/cover tended to be more influential, whereas, in watersheds with high transport capacity, land use/cover across the entire watershed was important for explaining lake chemistry. Thus, although land use is a key driver of nutrient loading to lakes, the extent to which it influences water quality can vary with watershed transport capacity.
Bibliographical noteFunding Information:
This work benefited from discussions with Lucinda Johnson and Mike Burkhart. Thanks are due to George Antoniou, Jessica Davis, Jingyang Li, and Zsolt Gemesi for technical support, and to Pat Soranno, Erik Jeppesen, and three anonymous reviewers for their comments on an earlier draft of this manuscript. Funding for our study was provided by the Iowa DNR. JMF was supported by the National Research Initiative of the USDA-CSREES, grant #2005-35102-16291.
- Landscape configuration
- Riparian areas
- Water chemistry