02025nas a2200145   4500008004100000022001400041245012000055210006900175300000900244490000600253520153700259100002001796700002201816856004101838       2014                        eng d  a2044-204100aWater quality implications from three decades of phosphorus loads and trophic dynamics in the Yahara chain of lakes0 aWater quality implications from three decades of phosphorus load  a1-140 v43 aTrophic responses to phosphorus (P) loads spanning 29-33 years were assessed for the eutrophic Yahara chain of lakes: Mendota (area = 39.6 km(2), mean depth = 12.7 m, flushing rate = 0.23 yr(-1)); Monona (13.7 km(2), 8.3 m, 1.3 yr(-1)); Waubesa (8.5 km(2), 4.7 m, 4.3 yr(-1)); and Kegonsa (13.0 km(2), 5.1 m, 3.0 yr(-1)). During extended drought periods with low P loads, summer (Jul-Aug) total P (TP) concentrations declined substantially in all 4 lakes, with Mendota achieving mesotrophic conditions (<0.024 mg L-1). In years when P loads were high due to major runoff events, summer TP in the lakes was high (especially in shallower Waubesa and Kegonsa); in some summers dissolved inorganic P was elevated, indicating algae growth was not P limited. Summer TP returned to normal levels following both low and high load years, signifying the lakes were responsive to P load changes. The proportion of P input loads passed via a lake's outlet to the next lake downstream increased as flushing rates increased. Because Monona, Waubesa, and Kegonsa received 60, 83, and 76% of their surface water P load from the respective upstream lake's outlet, reducing P loads in Mendota's large watershed was predicted to produce significant water quality benefits downstream. Modeling indicated a significant grazing effect of Daphnia on summer TP and Secchi transparency readings for Mendota and Monona. Finally, using drought loads as targets, our study established P loading reductions needed to improve water quality in all 4 Yahara lakes.1 aLathrop, R., C.1 aCarpenter, S., R.  uhttp://dx.doi.org/10.5268/iw-4.1.680