5/18/2015  |   15:30 - 15:45   |  102C

VARIABLE COUPLING OF CARBON, NITROGEN, AND PHOSPHORUS CONCENTRATIONS DURING BASEFLOW AND STORMS IN A SUBURBANIZING WATERSHED The carbon (C), nitrogen (N), and phosphorus (P) cycles are strongly coupled but humans are changing the nature of the coupling. Previous studies revealed coupled relationships between nitrate-N (NO₃-N) and both dissolved organic C (DOC) and phosphate (SRP) in streams during baseflow. However, non-point exports occur predominantly during storms and C-N-P dynamics during episodic events are not well understood. We used in situ sensors to simultaneously measure DOC, NO₃-N, SRP, and chloride (Cl), a conservative tracer, in a suburbanizing New Hampshire watershed (479 km²) between April and December 2011 to determine whether C-N-P coupled export changes during storms. DOC and NO₃-N concentrations had an inverse relationship under baseflow conditions, similar to previous findings, but often became positively correlated during storms. NO₃-N increased with Cl during both baseflow and storms, while DOC declined with increasing Cl. NO₃-N and SRP were positively correlated throughout the study, but the relative timing of peak N and P concentrations varied. The transport of C-N-P during storms contrasts with microbially mediated processes during baseflow that can affect the apparent coupling of C-N-P exports from watersheds.

Richard Carey (Primary Presenter/Author), University of New Hampshire, richard.carey@unh.edu;


Wilfred M. Wollheim (Co-Presenter/Co-Author), University of New Hampshire, wil.wollheim@unh.edu;


Gopal Mulukutla (Co-Presenter/Co-Author), University of New Hampshire, gopal.mulukutla@unh.edu;

5/18/2015  |   15:45 - 16:00   |  102C

WATERSHED LAND USE EFFECTS ON COUPLED NITROGEN AND PHOSPHORUS RELATIONSHIPS IN U.S. STREAMS AND RIVERS Strategies to establish nutrient criteria for streams and rivers currently overlook coupling of nitrogen (N) and phosphorus (P) concentrations and how relative N and P availability changes with land use and stream size. We analyzed publicly available data for patterns in total and dissolved inorganic N and P (TN, TP, DIN, DIP) concentrations by watershed area and land-use category. Highest mean TN and DIN concentrations were in agricultural watersheds (4.3 and 3.3 mg L-1, respectively; ANOVA P<<0.05); highest mean TP and DIP concentrations were in urban watersheds (0.33 and 0.19 mg L-1, respectively; ANOVA P<<0.05). Relative molar ratios of N and P followed this pattern: streamwater N:P was higher in agricultural (153:1) vs. urban watersheds (72:1; ANOVA P<<0.05). N:P ratios in particulate matter indicated stoichiometric control of uptake of excess nutrients, especially of N. Particulate N:P was relatively invariant across streamwater N:P availability, implying stoichiometric regulation of N and P uptake. Our analysis reveals a robust signature of stoichiometric coupling of N and P uptake in streams and rivers, explaining patterns in nutrient export with increased N and P loading.

David W. P. Manning (Primary Presenter/Author), The Ohio State University, manning.413@osu.edu;


Amy D. Rosemond (Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;


Jonathan P. Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;


John S. Kominoski (Co-Presenter/Co-Author), Florida International University, jkominoski@gmail.com;


Phillip Bumpers (Co-Presenter/Co-Author), University of Georgia, bumpersp@gmail.com;

5/18/2015  |   16:00 - 16:15   |  102C

LONG-TERM PHOSPHORUS TRENDS IN WISCONSIN LAKES Anthropogenic nutrient loading is a major stressor of lakes worldwide. Although watershed management efforts have reduced nutrient loading, eutrophication may worsen as agriculture expands, land develops, and precipitation intensifies. The Wisconsin Department of Natural Resources has been collecting total phosphorus (TP) on 62 lakes for up to 45 years, providing an opportunity to test whether phosphorus concentrations have changed over time. These lakes occur throughout the state in agricultural, urbanized, and forested watersheds and range in size, trophic status, and hydrology. I used linear models to test for change in annual mean TP over time. Total phosphorus significantly increased in 6 lakes, decreased in 8 lakes, and did not change in 44 lakes. Lakes with a decreasing trend were located in southern Wisconsin watersheds with significantly more developed land. Most lakes with an increasing trend were deep and in forested, northern watersheds. Long-term data sets such as this one elucidate trends in time and space and provide opportunity to understand causes of change, be they environmental drivers or the result of direct management actions.

Catherine Hein (Primary Presenter/Author), Wisconsin Department of Natural Resources, catherine.hein@wisconsin.gov;