Spatial Distribution of Land Type in Regression ...

ECOLOGY AND POPULATION BIOLOGY Reference: Biol. Bull. 207: 173. (October 2004) © 2004 Marine Biological Laboratory

Spatial Distribution of Land Type in Regression Models of Pollutant Loading Evan J. Fedorko1, R. Gil Pontius, Jr.1, Stephen P. Aldrich2, Luc Claessens3, Charles Hopkinson, Jr.4, and Wilfred M. Wollheim5 1 Clark University, Worcester, Massachusetts 2 Michigan State, East Lansing, Michigan 3 San Diego State, San Diego, California 4 Marine Biological Laboratory, Woods Hole, Massachusetts 5 University of New Hampshire, Durham, New Hampshire We propose a method to improve landscape-pollution interaction regression models by including a variable that describes the spatial distribution of a land type with respect to the pattern of runoff within a drainage catchment. The proposed indicator is used as an independent variable to enhance the strength, as quantified by R2 values, of regression relationships between empirical observations of instream pollutant concentrations and land type, by considering the spatial distribution of key land-type categories within the sample point’s drainage area. We present an indicator that, when used in conjunction with a variable describing the proportion of the land type, adds a new dimension of explanatory power. We demonstrate the usefulness of this indicator by exploring the relationship between nitrate (NO⫺ 3 ) and land type within 40 drainage sub-catchments in the Ipswich River watershed, Massachusetts. Nutrient loads associated with non-point source pollution paths are related to land type within the drainage catchments of sample sites. Past studies have focused on the quantity of a particular land type within a sample point’s drainage catchment. Quantifying the spatial distribution of key land-type categories in terms of location on a runoff surface improves our understanding of the relationship between sampled NO⫺ 3 concentrations and land type. Regressions that employ the proportion of residential land type within catchments provide a fair fit (R2 ⫽ 0.67). However, we find that a regression including a variable that indicates the spatial distribution of residential land improved the overall relationship between in-stream NO⫺ 3 measurements and associated land type (R2 ⫽ 0.712). We test the sensitivity of the results with respect to variations in the index definition in order to determine the conditions under which the spatial indicator variable is worthwhile.

173

Reference: Biol. Bull. 207: 173. (October 2004) © 2004 Marine Biological Laboratory

Estimating Groundwater-Derived Nitrogen Flux Into a Coastal Embayment: Salt Pond, Cape Cod, Massachusetts Kayla Halloran1, Matt Charette2, Paul Henderson2, Kevin Kroeger2, Lindsey Ryckman3, John Crusius3, and Dirk Koopmans3 1 Bucknell University, Lewisburg, Pennsylvania 2 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 3 United States Geological Survey, Woods Hole, Massachusetts Submarine groundwater discharge (SGD) often contributes significant fluxes of nutrients to coastal waters and is an important vehicle for nitrogen transport. Salt Pond, a small eutrophic coastal embayment in Cape Cod, Massachusetts, is connected by a single outlet to the Nauset Marsh System and receives elevated anthropogenic nitrogen inputs associated with human development. A series of seepage meter deployments found that SGD was not related to tidal stage, suggesting that the groundwater hydraulic head is above the sea level at all times. The average SGD rate from seepage meters of 12 cm d⫺1 was comparable to a similar concurrent experiment, which employed radon as a tracer of SGD (4 cm d⫺1). Groundwater sampling indicated that nitrate was transported conservatively through the aquifer, suggesting that little denitrification occurs during the mixing of fresh and salty groundwater. Using the seepage meter flow rates and average total dissolved nitrogen (TDN) concentrations in the groundwater, the SGD-derived TDN flux to the pond was 11.5 mmol m⫺2 day⫺1 (67% as nitrate, 30% as dissolved organic nitrogen, 3% as ammonium). Surface water sampling in the tidally flushed channel over a tidal cycle revealed that the Nauset Marsh is a net source of TDN to Salt Pond (12.7 mmol m⫺2 day⫺1). Thus, Salt Pond is a net nitrogen sink, with a total of 24.2 mmol m⫺2 day⫺1 being retained by the system, most likely in the form of algal biomass and denitrification in the fine-grained organic rich sediments that characterize the deep basin.

174

ABSTRACTS FROM THE MBL GENERAL SCIENTIFIC MEETINGS

Reference: Biol. Bull. 207: 174. (October 2004) © 2004 Marine Biological Laboratory

Reference: Biol. Bull. 207: 174. (October 2004) © 2004 Marine Biological Laboratory

Effect of Nutrient Enrichment and Salinity on Salt Marsh Invertebrates in the Plum Island Estuary Jenn Kerry1, Dorothy Boorse1, and Robert Buchsbaum2 1 Gordon College, Wenham, Massachusetts 2 Massachusetts Audubon Society, Wenham, Massachusetts

Alkaline Phosphatase Activity in the Toxic Dinoflagellate Karenia brevis Allison C. Craney1, S. T. Haley, and S. T. Dyhrman2 1 Mount Holyoke College, South Hadley, Massachusetts 2 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

Nutrient enrichment of tidal marshes accompanies landscape development and urbanization. Such enrichment can alter tidal marsh communities. As part of the Plum Island Long Term Ecological Research project, we investigated the impact of a sewage outfall in Greenwood Creek marsh, Ipswich, Massachusetts, on litter-inhabiting macroinvertebrates. Because the sewage outfall also introduced fresh water to the Greenwood marsh, we compared it to two reference marsh systems: one brackish and one marine. Mesh litterbags were filled with Spartina patens litter and placed in three vegetation zones [high marsh (Spartina patens), low marsh (Spartina alterniflora), and upland edge vegetation]. The stands of edge vegetation were of two types: Typha angustifolia in the brackish marsh and Phragmites australis in the sewage outfall marsh. Bags were incubated in each marsh system during two different twoweek intervals, and after each interval, we collected and counted the invertebrates that had entered. We also compared the invertebrates caught in two types of litterbags (cloth and plastic mesh). There were more individuals and more taxa in the brackish reference marsh than in the sewage outfall marsh, both of which had more individuals and taxa than the marine marsh. Greenwood Creek marsh had the highest nitrogen load of the three marshes, but the average salinity on the marsh was similar to the marine marsh. Fauna colonizing litterbags may be negatively affected by high salinity. This may have offset the expected increase in invertebrates due to nutrient loading in the Greenwood Creek marsh. There were lower abundances of individuals in the P. australis edge vegetation zone than in any other vegetation zone, but there was no effect of vegetation on taxonomic richness. More individuals were collected during the second two-week experiment. In the comparison between litterbag types, abundances of individuals and taxonomic richness were higher in the cloth mesh bags than in the plastic mesh bags. The plastic mesh bags had slightly smaller openings, and a large area was covered by a label through which fauna could not pass. This work was supported by an NSF-REU (OCE 9726921). We are indebted to Kelsey Correa for field assistance and to the TIDE (NSF DEB 0213767) project for equipment.

Over the past two decades, there has been an increase in both the occurrence and geographic extent of harmful algal blooms such as those of the toxic dinoflagellate Karenia brevis, further perpetuating threats to marine environments and to human health. K. brevis can cause neurotoxic shellfish poisoning (NSP) and respiratory irritation in humans. Blooms of K. brevis are common off the coast of Florida and seriously impact local economies when they occur. Despite its importance, little is known about how K. brevis acquires phosphorus, a nutrient critical to dinoflagellate nutrition. In this study, the enzyme alkaline phosphatase was examined. This is an enzyme that hydrolyzes organic phosphorus into a bioavailable form, typically after inorganic phosphate has been depleted. Axenic K. brevis CCMP 2281 cultures were grown in triplicate treatments of nutrient replete, low nitrogen (50 ␮M), and low phosphorus (1 ␮M) L1 medium. Alkaline phosphatase activity (APA) was assayed using both bulk and cell-specific (Enzyme Labeled Fluorescence) methods. Cell-specific assays suggested that APA in low phosphorus treatments was five-fold higher on average than the nutrient replete treatments, and almost four-fold higher than the low nitrogen treatments. Bulk assays corroborated a higher rate of APA in the low phosphorus treatments relative to the controls.

ECOLOGY AND POPULATION BIOLOGY Reference: Biol. Bull. 207: 175. (October 2004) © 2004 Marine Biological Laboratory

175

Reference: Biol. Bull. 207: 175. (October 2004) © 2004 Marine Biological Laboratory

Nitrate Reductase and Glutamine Synthetase Activity and Growth in Ulva lactuca in Waquoit Bay: A Time Sequence of Responses to Differences in Nitrogen Supply Leanna R. Heffner, Mirta Teichberg, Sophia Fox, and Ivan Valiela Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts

Life History Analysis of the Juvenile Horseshoe Crab in Pleasant Bay, Cape Cod Sarah B. Cierpich1, Sara P. Grady2, and Ivan Valiela2 1 University of Massachusetts, Amherst, Massachusetts 2 Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts

Opportunistic macroalgae often bloom in waters receiving increased nitrogen inputs as a result of anthropogenic activity. To assess the growth of Ulva lactuca, a bloomforming macroalga, to differences in nitrogen supply, we carried out cage incubations in two Cape Cod estuaries with different nitrogen loads, and enriched half of the algal fronds with nitrate. We measured the enzyme activities involved in nitrogen assimilation—nitrate reductase (NR) and glutamine synthetase (GS)—to assess nitrogen uptake in Ulva from the two estuaries for the different treatments. In addition, percent tissue nitrogen (N), stable isotopic signatures, and growth rates of the algae were measured. Nutrient analyses showed that nitrate concentrations were higher in the enriched cages than in the controls, and ammonium concentration did not vary between treatments. Over the course of the incubation, NR levels were significantly higher in algae from the high N-load estuary than from the low N-load estuary; and in both estuaries activity increased with nitrate enrichment. GS activity was similarly variable among all treatments. Percent tissue N in the enriched algae and algae from the high N-load estuary was higher than the controls and the algae from the low N load; and the isotopic signatures signaled a rapid turnover of nitrogen in the enriched algal fronds because they quickly incorporated the nitrate fertilizer into their tissue. After a 15-day incubation period, percent growth of U. lactuca in both estuaries was greater in the nitrate-enriched cages compared with the control cages. The growth observed in the enriched algae at the end of the incubation may be a response to increased NR activity, tissue N content, or both. These results corroborate observations that increased inputs of nitrate into estuarine waters rapidly stimulate growth of opportunistic macroalgae, such as U. lactuca, thus contributing to increasing occurrences of macroalgal blooms.

Little is known about the early life history of the Atlantic horseshoe crab (Limulus polyphemus), and few studies have been done regarding its life history—specifically, first-year juvenile growth rate and mortality rate. Quadrat surveys were completed along transects perpendicular to the hightide line in the intertidal zone of Pleasant Bay during low tide every semilunar period from mid-May through midAugust. The prosomal widths of the crabs were measured and recorded. The number of crabs found during the survey period increased, peaking in mid-July, indicating that peak spawning occurred in late June or early July. The spawning season for horseshoe crabs appears to have begun in mid to late March and appears to have ended in early August. The survey results also showed clear size differences between cohorts. An entire cohort was barely found during the survey, which suggests either impaired spawning or egg mortality due to weather conditions in late May. Growth and mortality rates declined with increasing juvenile crab size and age. This study provides information on the life history of juvenile horseshoe crabs, which can be useful in fisheries management and in the development of further life history studies of juvenile horseshoe crabs.