Macrophyte Abundance in Waquoit Bay: Effects of Land-Derived Nitrogen Loads on Seasonal and Multi-Year Biomass Patterns

Abstract

Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems.To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for six years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha -1 y -1 . Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries, but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the six years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely Fox et al. 3 overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.

Characteristics of early eutrophication encoded in submerged vegetation beyond water quality: a case study in Lake Erhai, China

“…In Haichao Bay, biomass and coverage of submerged vegetation did not vary substantially between seasons because the dominant P. maackianus is perennial and can overwinter in this bay. In temperate estuaries, Fox et al (2008) found that seasonal biomass of macrophyte stands was more variable in nutrient-rich bays than in infertile bays, in line with our observation in Lake Erhai. Generally, ecological functions of submerged macrophytes depend on percentage of volume infested (PVI) by the plants and their vegetative longevity in growing season (Schutten et al 1994;Sayer et al 2010).…”

“…and Ceratophyllum demersum to Potamogeton pusillus, Potamogeton pectinatus and Zannichellia palustris in some European shallow lakes in the progress of eutrophication (Sayer et al 2010;Hilt et al 2013). Hence, changes in the submerged macrophyte community can provide useful information in indicating responses of shallow lake ecosystems to early eutrophication and shifts between alternative states (Fox et al 2008;Penning et al 2008;Søndergaard et al 2010;Sayer et al 2010). Therefore, it is necessary to examine responses of both water quality and submerged macrophytes to external nutrients loading to find out more suitable indicators for early eutrophication.…”

Ocorrência de Ulva spp., Polysiphonia sp., e Microcystis aeruginosa nas praias do Saco do Laranjal, Pelotas, RS

“…Embora neste trabalho não conste valores de nu-trientes, para avaliar o grau de trofia, foi possível observar uma das consequências mais graves deste processo, as florações, que normalmente são relacionadas a processos de eutrofização (Sfriso et al, 1992;Paerl et al, 2001;Santos et al, 2006;Fox et al, 2008).…”

Forest Bird Populations in Massachusetts: Breeding Habitat Loss and Other Influences

“…The third sub-estuary, the Quashnet River delivers 403 kg N/ha per year (358 lbs N/acre per year). Macrophyte biomass has increased in proportion to nitrogen loading (Fox et al, 2008).…”