Abstract: An updated assessment of nutrient related impacts in US estuaries was completed in 2007. This assessment evaluates three components for each estuary: the influencing factors (e.g. land use, nutrient loads), the overall eutrophic condition (e.g. chlorophyll a, presence of nuisance/toxic algae and macroalgae, extent of dissolved oxygen problems, loss of submerged aquatic vegetation), and future outlook. Eutrophication is a widespread problem with 65% of assessed systems showing moderate to high level problems. The most impacted region was the mid-Atlantic. The majority of estuaries assessed, with the exception of North Atlantic systems (Cape Cod north to Maine), are highly influenced by human related activities that contribute to land-based nutrient loads. Conditions were predicted to worsen in 65% and to improve in 19% of the assessed estuaries in the future. Analysis of the extent of change from the early 1990s to the early 2000s, for those systems for which sufficient data were available, shows that conditions mostly remained the same (32 of 58 systems) though changes were observed in several smaller systems; 13 systems improved and 13 systems worsened. Chlorophyll a and HAB impacts have increased in the mid-Atlantic region, the only region with data adequate for comparison. These symptoms are more prevalent in systems with longer residence times, such as coastal lagoons. The successful restoration of seagrass in Tampa Bay is encouraging though future management to sustain the recovery will be difficult given expected population increases. This national assessment illustrates the need for coordinated and integrated action that balances management action, efficient monitoring to assess the effectiveness of the management, focused research, and a communication campaign aimed at engaging the broader community.

Abstract: Nitrogen loading to aquatic ecosystems from sewage is recognised worldwide as a growing problem. The use of nitrogen stable isotopes as a means of discerning sewage nitrogen in the environment has been used annually by the Ecosystem Health Monitoring Program in Moreton Bay (Australia) since 1997 when the technique was first developed. This (“sewage plume mapping”) technique, which measures the δ¹⁵N isotopic signature of the red macroalga Catenella nipae after incubation in situ, has demonstrated a large reduction in the magnitude and spatial extent of sewage nitrogen within Moreton Bay over the past 5 years. This observed reduction coincides with considerable upgrades to the nitrogen removal efficacy at several sewage treatment plants within the region. This paper describes the observed changes and evaluates whether they can be attributed to the treatment upgrades. (c) 2004 Published by Elsevier Ltd.

Abstract: Nitrogen loading from anthropogenic sources, including fertilizer, manure, and sewage effluents, has been linked with declining water quality in coastal lagoons worldwide. Freshwater inputs to mid-Atlantic coastal lagoons of the USA are from terrestrially influenced sources: groundwater and overland flow via streams and agricultural ditches, with occasional precipitation events. Stable nitrogen isotopes ratios (delta N-15) in bioindicator species combined with conventional water quality monitoring were used to assess nitrogen sources and provide insights into their origins. Water quality data revealed that nutrients derived from terrestrial sources increased after precipitation events. Tissues from two bioindicator species, a macroalgae (Gracilaria sp.) and the eastern oyster (Crassostrea virginica) were analyzed for delta N-15 to determine spatial and temporal patterns of nitrogen sources. A broad-scale survey assessment of deployed macroalgae (June 2004) detected regions of elevated delta N-15. Macroalgal delta N-15 (7.33 +/- 1.15aEuro degrees in May 2006 and 6.76 +/- 1.15aEuro degrees in July 2006) responded quickly to sustained June 2006 nutrient pulse, but did not detect spatial patterns at the fine scale. Oyster delta N-15 (8.51 +/- 0.89aEuro degrees) responded slowly over longer time periods and exhibited a slight gradient at the finer spatial scale. Overall, elevated delta N-15 values in macroalgae and oysters were used to infer that human and animal wastes were important nitrogen sources in some areas of Maryland's coastal bays. Different nitrogen integration periods across multiple organisms may be used to indicate nitrogen sources at various spatial and temporal scales, which will help focus nutrient management.

Abstract: Increasing eutrophication of coastal marine environments has led to the development of nutrient sampling programs to monitor water quality. Various shortcomings of chemical analyses have identified the need to develop biological indicators (bioindicators) that can be used to detect available nutrient concentrations. Macroalgal tissue nutrient content, pigments, and amino acids appear to be responsive to water column nutrient availability. The responses of the red alga, Gracilaria edulis (Gmelin) Silva, were related to nitrogen (N) source and availability in laboratory and field incubations to identify characteristics that would serve as bioindicators of N. The amino acid, pigment, and tissue N composition of G. edulis was analysed after incubation in different N sources (NH₄⁺, NO₃^-, and urea) and a range of [NH₄⁺] in laboratory aquaria. These results were compared to field responses after incubation of G. edulis along a N gradient in the Brisbane River (3 sites) and Moreton Bay (5 sites), Queensland, Australia. Photosynthetic pigments (phycoerythrin and chlorophyll a) increased in laboratory experiments, in response to increasing [NH₄⁺], but not [NO₃^-] or [urea]. Phycoerythrin was observed to be the more responsive of the two. Total tissue N increased linearly with increasing [NH₄⁺] in the laboratory but did not respond to [NO₃^-] or [urea]. In the field both phycoerythrin and tissue N appeared to respond equally to NH₄⁺ and NO₃^- availability. The amino acid composition provided the best representation of the concentration and source of available N. Citrulline was the most responsive of all amino acids to changes in concentrations of available N, with citrulline concentrations increasing linearly (r² = 0.84) with [NH₄⁺] in laboratory experiments. NH₄⁺ treatments produced increases in citrulline, phenylalanine, serine and free NH₄⁺, and decreases in alanine; NO₃^- treatments produced increases in glutamic acid, citrulline and alanine; urea treatments produced increases in free NH₄⁺ and decreases in phenylalanine and serine. The observed variations in amino acid content facilitated the development of an index for each N source based on relative concentrations of various amino acids. The N source index was used to predict the dominant source of N being assimilated by the macroalgae (i.e., metabolic profiling). Results demonstrated strong correlations between the N source index value and water column nitrogen concentrations (r² = 0.99 for NO₃^- and r² = 0.79 for NH₄⁺) in Brisbane River field trials. In Moreton Bay where dissolved inorganic nitrogen values were low (<2 mM), N source indices proved valuable in identifying predominant N sources. Physiological responses to N by this macroalga could be related to N source and availability in both laboratory and field situations, thus providing a sensitive bioindicator of N. In particular, the analysis of macroalgal amino acid content to infer the source and availability of N in a variety of field situations, appears to be a very sensitive biological indicator.

Abstract: A submersible pulse amplitude modulated (PAM) fluorometer was used to determine the effects of desiccation, ultraviolet radiation, changes in solar radiation and nutrient availability on the photosynthetic apparatus of a variety of marine plants (zooxanthellae, benthic microalgae and macroalgae) at Heron Island, Great Barrier Reef, Australia. The PAM measures photosynthesis as irradiance-dependent photosystem II electron transport. There were a number of interspecific and intraspecific variations in electron transport rate (ETR) based on physiological and morphological differences, and the plant's response to changes in environmental conditions. The highest ETR was found in the zooxanthellae of the clam Tridacna maxima, and the lowest in the calcified green macroalga Halimeda opuntia. Factors such as water velocity, ultraviolet radiation, solar radiation (total irradiance and spectral changes), desiccation, nutrient availability and algal pigment content were hypothesised as influencing intraspecific changes in ETR. A series of experimental manipulations were conducted to test these hypotheses. Reef flat algae was shaded to 50% of incident solar radiation and 0% of ultraviolet radiation. Samples of macroalgae were collected from the reef flat and 15 m depth and allowed to desiccate to determine if different populations of the same species could adapt physiologically to different environmental conditions. Reef flat samples were collected and incubated in seawater enriched in nitrogen and phosphorus to test for nutrient limitation. Significant differences in the ETR of the plants tested highlighted the impacts of various environmental parameters on photosynthetic capacity. Samples from regions with higher water velocities on the reef flat had significantly higher ETRs. Screening of ultraviolet radiation increased the maximum ETR of certain species, while prolonged periods of shading reduced the maximum ETR of some species more quickly than others. Desiccation responses were the same between deep collected and reef flat populations, although increased light and temperature did reduce the maximum ETR of the deep collected samples. Fertilisation responses varied between species. The results indicate that PAM fluorometry can be used as a tool for in situ non destructive assessment of the effects of various ecological parameters on photosynthetic activity in marine plants.