Candace A. Oviatt

NUTRIENTS AND THE PRODUCTIVITY OF ESTUARINE AND COASTAL MARINE ECOSYSTEMS

SUMMARY Recent research on estuarine and coastal marine systems has revealed two particularly interesting things about nutrients and productivity. First is the observation that these areas are among the most intensively fertilized environments on earth. Second is the common finding that much of the characteristically high primary productivity of these shallow waters is supported by nutrients released or recycled by pelagic and benthic microheterotrophs. Since nutrient inputs to coastal areas have probably been increasing and are likely to continue to do so, it is particularly important to understand the relationship between nutrient loading and nutrient cycling and the extent to which their interactions may set the levels of primary and secondary production in coastal systems. That some direct relationship exists between the input of nutrients and the productivity of higher trophic levels has been a principle of marine ecology since the turn of the century. It is surprisingly difficult, however, to find q...

EFFECTS OF THE SPAWNING MIGRATION OF THE ALEWIFE, ALOSA PSEUDOHARENGUS, ON FRESHWATER ECOSYSTEMS'

The influx of large numbers of alewife, Alosa pseudoharen gus, into relatively small freshwater systems may have a considerable impact upon pre-established food chains and nutrient cycles. We estimate the total nutrient input to Pausacaco Pond, Rhode Island, USA, from alewives amounted to 0.43 g P. 2.7 g N, and 16.8 g C/M2 over a 2-mo period. This is largely through mortality of the spawning fish, and to a lesser extent through excretion. These inputs were much greater than the eventual nutrient loss to the system through emigration of juvenile fish. In tank experiments using pond microcosms, the initial response to the addition of the fish was a large phytoplankton bloom and an increase in litter respiration. The phytoplankton bloom was short- lived, and the most lasting effect was an increase in production and respiration in the leaf litter. This increased production in the litter community would support a long lasting supply of insect and benthic invertebrate food for young fish. The respiration rate of autumn leaves incubated in alewife streams during the migration was significantly higher than that of leaves incubated simultaneously in a stream which had no alewife run. Respiration rates of leaves incubated in the same streams before the arrival of alewives did not differ significantly. The increase in litter respiration, an indication of microbial and invertebrate activity on the leaf surface, was attributed to the additional nutrients supplied by the fish.

The changing ecology of temperate coastal waters during a warming trend

In the temperate North Atlantic Ocean the ecological changes in coastal waters associated with a warming period in the 1930s were compared with the past couple of decades when the North Atlantic Oscillation was also positive. Long-term monitoring data sets from Rhode Island and nearby coastal waters were used to identify trends in the recent warming period. During both events winter water temperatures warmed above a mean value of 2.9°C from 1°C to 3°C. There was no apparent trend in the annual salinity cycle correlated with the increased temperature. During both periods boreal species declined, southern species increased, and widespread declines in eelgrass occurred. Estuaries on the western Atlantic Ocean during the recent warming period had phytoplankton biomass during the winter-spring bloom decrease, zooplankton number increase, and nutrients remain elevated due to enhanced zooplankton grazing. Zooplankton numbers decreased in summer due to enhanced ctenophore predation. In these waters the loss of boreal demersal fish has been compensated by an increase in demersal decapods. The very large ecological changes caused by small increases in seasonal temperature provide an insight to the large alterations that may be associated with global warming.

Coastal Lagoons and Climate Change: Ecological and Social Ramifications in U.S. Atlantic and Gulf Coast Ecosystems

Lagoons are highly productive coastal features that provide a range of natural services that society values. Their setting within the coastal landscape leaves them especially vulnerable to profound physical, ecological, and associated societal disturbance from global climate change. Expected shifts in physical and ecological characteristics range from changes in flushing regime, freshwater inputs, and water chemistry to complete inundation and loss and the concomitant loss of natural and human communities. Therefore, managing coastal lagoons in the context of global climate change is critical. Although management approaches will vary depending on local conditions and cultural norms, all management scenarios will need to be nimble and to make full use of the spectrum of values through which society views these unique ecosystems. We propose that this spectrum includes pragmatic, scholarly, aesthetic, and tacit categories of value. Pragmatic values such as fishery or tourism revenue are most easily quantified and are therefore more likely to be considered in management strategies. In contrast, tacit values such as a sense of place are more difficult to quantify and therefore more likely to be left out of explicit management justifications. However, tacit values are the most influential to stakeholder involvement because they both derive from and shape individual experiences and beliefs. Tacit values underpin all categories of social values that we describe and can be expected to have a strong influence over human behavior. The articulation and inclusion of the full spectrum of values, especially tacit values, will facilitate and support nimble adaptive management of coastal lagoon ecosystems in the context of global climate change.

Sediment resuspension and deposition in Narragansett Bay

Abstract Monthly samples of sediments deposited in traps at three locations in Narragansett Bay, Rhode Island, showed a gradient in sediment activity that increased from an annual mean of 20 ± 8·8 g m−2 day−1 at the head of the estuary to 51 ± 16·7 g m−2 day−1 at the mouth. Deposited materials were significantly higher in total organic matter, organic carbon and nitrogen than near surface sediments on the bottom. These parameters showed a gradient that decreased toward the mouth of the bay, with organic matter dropping from 14 ± 1 to 10 ± 1% of the dry weight deposited; carbon from 5·4 ± 0·9 to 3·4 ± 1·0%; and nitrogen from 0·6 ± 0·1 to 0·4 ± 0·1%. The annual mean C N ratio was 8·2 in the lower bay and 8·7 in the upper bay. Deposited materials were dominated by particles in the silt size range from 4–60 μm and comprised for the most part resuspended bottom sediments rather than fresh inputs of material from the water column.

The demersal fish of Narragansett Bay: An analysis of community structure, distribution and abundance

Abstract Monthly samples of demersal fish were collected from nine regular and 13 occasional stations in Narragansett Bay, Rhode Island throughout a year. While over 9000 individuals representing 99 species were taken, the 10 most abundant species made up 91% of the catch. Taxonomic composition and dominance of the fish community were generally similar to that reported for adjacent Block Island Sound and Long Island Sound, though diversity was slightly higher in the bay. Winter flounder, Pseudopleuronectes americanus was by far the most abundant species, and accounted for 36% of the total catch. Multiple regression analysis of fish numbers and biomass for total catch and for the dominant flounder indicated that of 14 environmental variables considered, only depth, sediment organic content, temperature and wind speed were significant in explaining distribution within the bay. No clear pattern of fish abundance was apparent, except for higher diversity near the mouth of the bay. The mean annual standing crop of 117 ± 151 fish/acre and 28·5 ± 16·0 lbs/acre (wet weight) was comparable to values reported for a variety of New England coastal and offshore areas. The total biomass of fish remained remarkably constant throughout the year when compared to adjacent coastal environments, while the abundance of particular species varied substantially with season.

Diel Metabolism and Nutrient Dynamics in a Salt Marsh Embayment

Simultaneous measurements of the diel patterns of dissolved 02, pH-CO2. dis- solved organic nitrogen, ammonia, nitrite, nitrate, dissolved organic phosphorus, phosphate, and silicate were made on four occasions in a shallow salt marsh embayment (Bissel Cove, Narragansett Bay, Rhode Island, USA) that was closed to tidal water exchanges for 24-h periods. In spite of high rates of community photosynthesis and respiration, there appeared to be little diel change in dissolved nutrient concentrations, especially with respect to inorganic nitrogen. During summer and early fall, inorganic nutrients appeared to cycle within the sediment-detritus system of the embayment bottom, rather than being released to the over- lying water. This suggests that there would be little export of inorganic nutrients from the marsh during tidal exchanges with the estuary. The behavior of this marsh embayment con- trasts with reports from other marsh areas where large net imports or exports of nutrients have been observed. The concentrations of dissolved organic phosphorus and nitrogen were higher than inorganic forms, and showed substantial variation over each diel sampling period. The relationship between photosynthetic or respiratory gas exchange and nutrient cycling in waters influenced by benthic community metabolism is subtle and complex, and cannot be adequately approximated by simple models such as the Redfield ratio.

Effect of the hard clam Mercenaria mercenaria on benthic fluxes of inorganic nutrients and gases

The effect of the hard clam Mercenaria mercenaria (L.) on the exchange of dissolved nutrients (silicate, phosphate, ammonium, nitrate+nitrite) and gases (oxygen, carbon dioxide) across the sediment-water interface was examined in 1983 and 1984 using experimental mesocosms (13 m3), designed to simulate a shallow coastal ecosystem, that allow for reciprocal biogeochemical interactions between water column (5 m) and bottom sediments (∼30 cm deep). Benthic, fluxes, measured during a spring-summer warming period, were compared for mesocosms maintained either with added M. mercenaria (16 per m2, treatment) or without M. mercenaria (control) as a component of the benthic community. Fluxes were within the range observed for the (control) community in situ in mid-Narragansett Bay and exhibited the pattern of increasing flux with increasing temperature observed in nature. For dissolved inorganic (DIN=ammonia+nitrate+nitrite), analytical problems allowed comparison of fluxes only at the higher temperatures (∼17° to 22°C); average DIN fluxes were 57% higher in mesocosms with clams. Fluxes of other nutrients and gases were modelled as exponential functions of temperature (∼9° to 22°C) using a linear regression of the natural logarithm of flux upon temperature in both treatment and control situations. Differences between regression slopes and intercepts for conditions with and without clams were assessed by analysis of covariance. Slopes of the linearized temperature-flux relationships were not significantly different between treatments for any flux measured, suggesting that presence of the clams did not alter the basic relationship of flux and temperature normally observed with this community. For oxygen consumption and silicate production, the regression intercepts were significantly higher in the clam treatment, suggesting that the level of flux was generally elevated in the presence of M. mercenaria by about 20% (oxygen) and 86% (silicate) at any given temperature. Data for carbon dioxide and phosphate showed similar trends to oxygen and silicate, but the variance in fluxes was larger and regression intercepts for the two treatments were not significantly different.

Mass and metabolism of a mussel bed

SummaryA mussel bed dominated by Mytilus edulis contained large concentrations of living consumer biomass, with over 14 kg dry weight/m2 distributed among eleven species. An additional 14.4 kg dry weight/m2 was present as empty shell fragments that contributed to community structure. Field measurements of community respiration for this dense animal system showed a roughly hyperbolic response to increasing current speed. In still water, oxygen uptake was 0.2g O2/m2/hr while in currents over 0.1 m/sec it quickly rose to about 2.7 g O2/m2/hr.

Analysis of Local Variation in the Standing Crop of Spartina alterniflora

Measurements of standing crop biomass and height of the tzll form of Spartina alterniflora on twelve Rhode Island salt marshes suggest that the nutrients in municipal sewage inputs may increase growth oi the grass. Spartina biomass in the Providence River and upper Narragansett Bay was 39°0 greater than in the lower by and 107°0 grcater than in Block Island Sound, Height of the plants increased 5% and 67% over those in the lower bay and sound, respcctively, Even with enhanced growth from eutrophication, calculations show that treatmcnt of marsh arcas with sewage cffluents is not a realistic hope for the recycling of wastes from coastal cities, or for providing low cost tertiary treatment. The mean dry weight at the end of the growing season was 840 ±_ 321 g;m for all marshes, with a ränge from 433 ± 80 g/m to 1380 i 220 g/m. Grass height averaged 112 i 28 cm on all sites, with a ränge from 50 ± 12 cm to 142 — 16 cm. Multiple regression analysis Indicated that concentrations of ammonia, sediment phosphorus, and sedimcnt nitrogen could account for 77% of the between site Variation in Spartina standing crop. Grass height was correlated with sediment iron in a manner suggesting this element äs a possible limiting factor. Half of the 12 marshes were significantly different from all other sites in terms of grass height, demonstrating the importance of having samptas frorn a variety of marshes in each area when analysis of large climatic gradients on production are attemptcd.