Abstract
This study focuses on soluble reactive phosphorus (SRP), a key driver of eutrophication worldwide and a potential contributor to the emerging global environmental problem of harmful algal blooms (HABs). Two studies of tributary SRP concentrations were undertaken in sub-watersheds of Cayuga Lake, NY, the subject of a total maximum daily load (TMDL) development process, due to phosphorus impairment of its southern shelf. The long-term study compared SRP concentration in Fall Creek in the 1970s with that in the first decade of the 2000s, thus spanning a period of change in phosphorus sources, as well as in regional climate. The spatial study used data collected between 2009 and 2018 and compared SRP concentrations in Fall Creek to levels in northeastern tributaries that flow into the lake close to areas where HABs have been problematic. SRP was measured using standard procedures. Flow-weighted mean SRP concentration ranged between 15.0 µg/L and 30.0 µg/L in all years studied in both the 1970s and 2000s, with the exception of 2010. Annual discharge in Fall Creek showed no trend between 1970 and 2018, but a higher proportion of high streamflow samples was captured in the 2000s compared to the 1970s, which resulted in proportionally increased SRP concentration in the latter time period. There was no significant difference in the SRP concentration—flow rate relationship between the two time periods. Adjusted for flow rate, SRP concentrations in Fall Creek have not changed over many decades. Increasing phosphorus contributions from growing population and urbanization since the 1970s may have been counterbalanced by improvements in wastewater treatment and agricultural practices. Mean SRP concentration in northeastern tributaries was significantly (p < 0.001) higher than in Fall Creek, likely reflecting more intense agricultural use and higher septic system density in the watersheds of the former. This finding justifies continued monitoring of minor northern tributaries. Future monitoring must emphasize the capture of high flow conditions. Historical stability and highly variable hydrology will slow the watershed response to management and confound the ability to detect changes attributable to decreased phosphorus inputs. Large scale monitoring on decadal timescales will be necessary to facilitate watershed management.
Highlights
Worldwide focus on the widespread problem of eutrophication has led to examination of the movement of nutrients from terrestrial to aquatic systems
A long-term study was undertaken to determine if there has been any change over a four decade period in soluble reactive phosphorus (SRP) concentration in Fall Creek, which drains the largest sub-watershed of the Cayuga Lake watershed in the Finger Lakes region of New York State
Our work is comprised of a long-term study of Fall Creek that compares its SRP concentrations in in the 1970s and in the 2000s, and a spatial study that compares SRP concentration in Fall Creek to the 1970s and in the 2000s, and a spatial study that compares SRP concentration in Fall Creek to that in that in northeastern tributaries of the watershed, 2009–2018
Summary
Worldwide focus on the widespread problem of eutrophication has led to examination of the movement of nutrients from terrestrial to aquatic systems. A long-term study was undertaken to determine if there has been any change over a four decade period in SRP concentration in Fall Creek, which drains the largest sub-watershed of the Cayuga Lake watershed in the Finger Lakes region of New York State. The study includes two divergent time periods between which significant changes have occurred in the Fall Creek and Cayuga Lake watersheds. More informal study in 2017 documented eastern shorelines as most affected [34] These observations provide the rationale for the examination of SRP in previously unexamined tributaries in the northeastern region of the Cayuga Lake watershed. Our work is comprised of a long-term study of Fall Creek that compares its SRP concentrations.
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