. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECOLOGY AND EVOLUTION 291 are based on DIN; to the extent that DON is labile, nitrogen loads calculated on the basis of land-derived DIN inputs alone underes- timate effective N loads (6, 7). There is evidence that urbanization of watersheds alters the lability as well as the amount of DON loaded to receiving waters (6). We evaluated these issues by use of estuaries of Waquoit Bay, Massachusetts (Sage Lot Pond, Quashnet River, and Childs River), that receive different N inputs from their watersheds because of different degre
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECOLOGY AND EVOLUTION 291 are based on DIN; to the extent that DON is labile, nitrogen loads calculated on the basis of land-derived DIN inputs alone underes- timate effective N loads (6, 7). There is evidence that urbanization of watersheds alters the lability as well as the amount of DON loaded to receiving waters (6). We evaluated these issues by use of estuaries of Waquoit Bay, Massachusetts (Sage Lot Pond, Quashnet River, and Childs River), that receive different N inputs from their watersheds because of different degrees of urbanization (1,4, 5). Sage Lot Pond (SLP) has a primarily forested watershed that provides a N load of 14 kg N ha"1 y~'; Quashnet River (QR) has a watershed with an intermediate degree of urbanization and a N load of 350 kg N ha" ' y~'; Childs River (CR) has a watershed with the greatest degree of urbanization, and a N load of 601 kg N ha"1 y~' (4, 5). To gain a better understanding of how urbanization alters DON. we measured the lability of DON from the three different estuaries. In each estuary we collected surface water from a station with a salinity of 25%t. Samples were placed in acid-washed bottles and kept on ice. The water was filtered through precombusted glass fiber filters to remove larger consumers and particulates. Triplicate samples (1000-ml/flask) were incubated at 25°C in the dark with continuous shaking. Each flask was re-sampled at 12. 24, 36, 48, 96, and 192 h. The water samples were filtered ( Durapore membrane Millipore filter, prerinsed with deionized water); placed in acid-washed, high-density polyethylene bottles; and frozen for later analysis. Nutrient concentrations were deter- mined by standard methods (Lachat QuikChem 8000 Automatic Ion Analyzer, 8). DON concentrations decreased in all incubations (Fig. 1, top right) and as a percentage of the total N (Fig. 1. middle row). The loss of DON generated NH4 + , which
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
