Nutrient enrichment of estuarine submersed vascular plant communities. 1. Algal growth and effects on production of plants and associated communities

Abstract

Eight experimental ponds containing submersed vascular plants (predominantly Potamogeton perfoliatus and Ruppja maritirna) were subjected in duplicate to 4 levels (including controls) of fertilization from June to August 1981. Seston and phytoplankton chlorophyll a increased with fertilization, and pronounced algal blooms were evident under high dosage. Of the total seston. phytoplankton exerted the greatest influence on attenuation of photosynthetically active radiation (PAR), such that there was insufficient light for submersed vascular plant growth at the sediment surface during bloonls. An extensive epiphytic community developed on plants in all nutrient-treated ponds at densities similar to those observed in nature on senescent plants. At high nutrient treatments the accumulation of epiphytic material resulted in > 80 % attenuation of the incident radiation at the leaf surface. Biomass of submersed macrophytes decreased significantly under high and medium nutrient treatments compared to control and low treatments within 60 d following initial fertilization. Apparent production of vascular plants (based on oxygen production and I4C-bicarbonate uptake) was reduced at the higher nutrient treatments for both R. maritirna and P. perfoliatus. Most of this reduction in macrophyte photosynthesis could be explained by attenuation of PAR associated with epiphytic material. However, without PAR attenuance in the overlying water, observed levels of epiphytic growth would be insufficient to reduce light below compensation levels needed to sustain vascular plant growth. At the high fertilization rates, integrated primary production of pond communities was significantly reduced with the loss of the vascular plants, even though phytoplankton and epiphytic growth were enhanced.

Discordance between living and death assemblages as evidence for anthropogenic ecological change

“…a common consequence of eutrophication: in addition to increasing epiphytic growth, nutrient enrichment increases phytoplankton production beyond zooplankton grazing capacity, leading to increased water turbidity, decreased light levels, and morbidity and mortality of subaquatic vegetation (6,27,28). The tendency for AE1 data sets to plot among pristine data sets makes sense in this regard, because fertilization initially stimulates grass growth.…”

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

“…Light is also attenuated by epiphytic material (algae, bacteria, invertebrates, detritus, and sediments) accumulating on SAV leaves. This epiphytic light attenuation can be characterized by the exponential coefficient, K e , which increases linearly with mass of epiphytic material (Twilley et al 1985). The slope of this relationship depends on the composition (e.g., chl adry weight) of the epiphytic material (Losee and Wetzel 1983;Staver 1984).…”

“…materials and to estimate associated light attenuation . Although the relative contribution of epiphytic material to total light attenuation for SAV can be measured directly (Twilley et al 1985), widespread monitoring of epiphyte attenuation (Stankelis et al 2003) would be prohibitively expensive for large estuaries such as Chesapeake Bay. We developed a quantitative function to estimate potential epiphyte contribution to total light attenuation for SAV at a particular depth from monitored water quality data for K d (m Ϫ1 ), TSS (mg l Ϫ1 ), DIN ( M), and DIP ( M).…”

“…Previous studies have made quantitative distinctions between water column and epiphytic contributions to total light attenuation (Twilley et al 1985;Vermaat and de Bruyne 1993).…”

“…Simple empirical correlations (Nielsen et al 2002) have been used to predict depth of maximum SAV biomass or colonization from routine water clarity measurements (Rørslett 1987;Zimmerman et al 1991;de Jonge and de Jong 1992). Although the widespread availability of water clarity data (e.g., Secchi disk depth) makes this a potentially useful approach, it does not account for light attenuation by epiphytes on SAV leaves, often a dominant factor in regulating plant growth (Twilley et al 1985;Sand-Jensen 1990). One approach to account for epiphytic shading is to monitor it directly in the field and to compute the combined effects of water clarity and epiphytes on total attenuation of light for SAV (Vermaat and de Bruyne 1993).…”