Betty A. Buckley

A Strikingly Rich Zone-Nutrient Enrichment and Secondary Production in Coastal Marine Ecosystems

Despite a recent review concluding that there is little or no reason to expect that the production of fish and other animals will increase with nutrient enrichment or eutrophication, there is a variety of evidence that anthropogenic nutrients can stimulate secondary production in marine ecosystems. Unique multiple-year fertilization experiments were carried out over fifty years ago in Scottish sea lochs that showed dramatic increases in the abundance of benthic infauna and greatly enhanced growth of fish as a result of inorganic nitrogen (N) and phosphorus (P) additions. These experiments appear to have provided a good qualitative model for the responses of the Baltic Sea to nutrient enrichment and resulting eutrophication. Historical comparisons by others have shown that the weight of benthic animals per unit area above the halocline in the Baltic is now up to 10 or 20 times greater than it was in the early 1920s and that the total fish biomass in the system may have increased 8 fold between the early part of the 1900s and the 1970s. While there are no similar data for the highly enriched central and southern North Sea, there is convincing evidence that the growth rates of plaice, sole, and other species have increased there since the 1960s or 1970s. Cross-system comparisons have also shown that there are strong correlations between primary production and the production and yield of fish and the standing crop and production of benthic macrofauma in phytoplankton-dominated marine ecosystems. Concerns over the growing nutrient (especially N) enrichment of coastal marine waters are clearly valid and deserve the attention of scientists and managers, but the recent demonizing of N ignores the fact that nutrients are a fundamental requirement for producing biomass. Decisions regarding the amount of N or P that will be allowed to enter marine ecosystems should be made with the full knowledge that there may be tradeoffs between increases in water clarity and dissolved oxygen and the abundance of oysters, clams, fish, and other animals we desire.

Reversal of the net dinitrogen gas flux in coastal marine sediments

The flux of nitrogen from land and atmosphere to estuaries and the coastal ocean has increased substantially in recent decades. The observed increase in nitrogen loading is caused by population growth, urbanization, expanding water and sewer infrastructure, fossil fuel combustion and synthetic fertilizer consumption. Most of the nitrogen is removed by denitrification in the sediments of estuaries and the continental shelf, leading to a reduction in both cultural eutrophication and nitrogen pollution of the open ocean. Nitrogen fixation, however, is thought to be a negligible process in sub-tidal heterotrophic marine systems. Here we report sediment core data from Narragansett Bay, USA, which demonstrate that heterotrophic marine sediments can switch from being a net sink to being a net source of nitrogen. Mesocosm and core incubation experiments, together with a historic data set of mean annual chlorophyll production, support the idea that a climate-induced decrease in primary production has led to a decrease in organic matter deposition to the benthos and the observed reversal of the net sediment nitrogen flux. Our results suggest that some estuaries may no longer remove nitrogen from the water column. Instead, nitrogen could be exported to the continental shelf and the open ocean and could shift the effect of anthropogenic nitrogen loading beyond the immediate coastal zone.

A one hundred and seventeen year coastal water temperature record from Woods Hole, Massachusetts

We have compiled what we believe is the longest coherent coastal sea surface temperature record in North America. Near-surface water temperature measurements have been made almost daily at Great Harbon, Woods Hole, Massachusetts, since 1886 with remarkably few gaps. The record shows that there was no significant trend in water temperature at this site for the first 60 yr of observation. There was some cooling during the 1960s that was followed by a significant warming from 1970–2002 at a rate of 0.04°C yr−1. During the 1990s annual mean temperatures averaged approximately 1.2°C warmer than they had been on average between 1890 and 1970; winter (December, January, and February) temperatures were 1.7°C warmer and summer (June, July, and August) temperatures were 1.0°C warmer. There has not been a statistically significant decrease in the annual number of winter days below 1°C or an increase in the annual number of winter days above 5°C. The number of summer days each year with water temperature above 21°C has not increased significantly. The dates of first observations of 10°C and 20°C water in the spring have not changed sufficiently to be statistically significant. There is a weak positive correlation between annual and winter water temperature and the annual and winter North Atlantic Oscillation index, respectively, during the period of record.

Responses of Very Shallow Marine Ecosystems to Nutrient Enrichment

The success of simple predictive relationships such as the Vollenweider plot in limnology has encouraged marine ecologists to attempt to develop similar models relating pollutant inputs to ecological conditions in estuaries. Most of these efforts have focused on relatively deep (>5 m) river mouth estuaries and embayments where primary production is dominated by phytoplankton. Experimental nutrient enrichment studies of phytoplankton-based mesocosms at the Marine Ecosystems Research Laboratory (MERL) have confirmed that simple Vollenweider type relationships can be found between the rate of input of inorganic nutrients and annual mean chlorophyll concentrations and primary production. However, much of the coastline of the U.S. is characterized by estuarine ecosystems that are very shallow, and where most of the primary production is carried out by angiosperms, such as eelgrass, Zostera marina, epiphytic algae, drift and attached macroalgae, and epibenthic microalgae, rather than by phytoplankton. We have not been able to find useful relationships between nutrient input and the type of plant providing most of the primary production or between nutrient input and the amount of primary production in such shallow lagoon systems. Attempting to adjust nutrient loading for varying hydraulic residence time did not improve the models. Experimental studies using shallow lagoon mesocosms have shown that there is a large variation in the abundance of the various plant forms in these very shallow systems, and that simple Vollenweider models are not likely to emerge for this type of environment. However, it does seem that total system production increases with nutrient enrichment at very low rates of input, and that eelgrass does not persist when exposed to even moderate levels of fertilization. Zostera responds to inorganic nitrogen enrichment and to shading by increasing the rate of leaf elongation and decreasing the allocation of resources to below ground roots and rhizomes. This reduces or eliminates lateral branching of the rhizomes and causes a decline in the density of shoots. Based on mesocosm studies, we propose several indicators of eelgrass health, including the rate of leaf elongation, plant density, and the shoot: root biomass ratio that all deserve further study and field testing.

Responses of epiphytes on eelgrass, Zostera marina L., to separate and combined nitrogen and phosphorus enrichment

Abstract We examined the effects of separate and combined nitrogen (N) and phosphorus (P) enrichment on the development of epiphytes on eelgrass (Zostera marina L.). The experiment used ten mesocosms as living models of shallow coastal lagoons along the southern shore of Rhode Island, USA. The mesocosms comprised, in duplicate, controls with no anthropogenic nutrient additions and four nutrient treatments: daily water column enrichment with phosphate alone (PO4), nitrate alone (NO3), nitrate plus phosphate (NO3 + PO4), or ammonium plus phosphate (NH4 + PO4). In the mesocosms enriched with PO4 alone, the epiphyte biomass, organic content, chlorophyll a content and community composition were as in the controls, but the nutrient content of the epiphytes (N and P) increased. Enrichment with NO3 alone increased chlorophyll a content, nutrient content, and relative abundance of cyanobacteria during the summer. Enrichment with NO3 + PO4 and with NH4 + PO4 produced intense and long lasting phytoplankton blooms that lowered epiphyte biomass and chlorophyll a content, but increased the N and P content of the epiphytes and the relative abundance of diatoms. There were no significant differences between the mesocosms enriched with NO3 + PO4 and those enriched with NH4 + PO4. Epiphyte biomass appears not to be a good indicator of nutrient loading or eutrophication in shallow coastal lagoons.

Impacts of temperature and nutrients on coastal lagoon plant communities

We investigated the independent and interactive effects of nutrient loading and summer water temperature on phytoplankton, drift macroalgae, and eelgrass (Zostera marina) in a coastal lagoon mesocosm experiment conducted from May through August 1999. Temperature treatments consisted of controls that approximated the 9-yr mean daily temperatures for Ninigret and Point Judith Lagoons in Rhode Island (United States) and treatments approximately 4°C above and 4°C below the controls. Nutrient treatments consisted of the addition of 6 mmol N m−2d−1 and 0.5 mmol P m−2 d−1 to mesocosms 4°C above and 4°C below the 9-yr daily mean. Nutrient enrichment produced marked phytoplankton blooms in both cool and warm treatments during early summer. These were replaced after midsummer by dramatic growths of macroalgal mats ofEnteromorpha flexuosa and, to a lesser degree,Cladophora sericea. No phytoplankton blooms were observed in the cool unenriched treatments, but blooms did develop in the mean temperature and warm mesocosms during the second half of the summer that were similar in intensity, though of shorter duration, than those observed earlier in the enriched systems. Macroalgal blooms did not occur in the unenriched mesocosms. Sustained warm water temperatures markedly decreased eelgrass density and belowground production and increased the time interval between the initiation of new leaves, particuarly when the biomass of macroalgae was high. The negative effect of elevated water temperature on eelgrass was significantly increased under conditions of elevated inorganic nutrient input. By the end of summer, virtually all of the measures of eelgrass health declined in rank order from cool, to mean, to cool enriched, to warm, to warm enriched treatments. It is likely that the marked declines in eelgrass abundance observed during recent decades in the Northeast have resulted from an interaction of increasing nutrient enrichment combined with increasing summer water temperatures.

Responses of Coastal Lagoon Plant Communities to Levels of Nutrient Enrichment: A Mesocosm Study

An experiment was conducted to quantify the effects of different levels of nutrient enrichment on the plant communities of temperate coastal lagoons, specifically the lagoons of the northeast U.S. Ten mesocosms, each containing coastal water, lagoon sediments, and plants and animals found in natural lagoons, were subjected to five levels of enrichment. Two mesocosms served as controls, and received no experimental nutrient additions. The remaining 8 mesocosms were enriched in duplicate with ammonium plus phosphate at 1.0 and 0.11 mmol N or P m−2 d−1, 2.0 and 0.19 mmol N or P m−2 d−1, 4.0 and 0.35 mmol N or P m−2 d−1, and 8.0 and 0.67 N or P mmol m−2 d−1. At all levels of enrichment, and through much of the experiment, water column concentrations of dissolved inorganic nitrogen (DIN) were drawn down to background levels. Despite the efficient drawdown of added DIN even at the highest loadings, differences in plant biomass among the 5 treatments were difficult to detect. Enrichment at the highest loadings increased standing stocks of phytoplankton for one month mid-experiment. No significant effect of loading could be detected for dry biomass of eelgrass (Zostera marina), epiphytic material, drift macroalgae, or for all plant components combined. The experiment has demonstrated that the enrichment responses of coastal lagoons can be diverse, especially at intermediate loadings.

Annual phytoplankton metabolism in Narragansett Bay calculated from survey field measurements and microcosm observations

Field surveys of phytoplankton metabolism, based on oxygen changes, were made in Narragansett Bay from 1971–73. Annual daytime net production varied from 218 g C per m2 per yr in the East Passage to 429 g C per m2 per yr in the Providence River. The area based average for the bay was 269 g C per m2 per yr. The area based average night respiration was 159 g C per m2 per yr resulting in an annual net carbon available for export or to the benthos of 110 g C per m2 per yr. A set of microcosms, operated so as to simulate the Bay, had an annual net production of 276 g C per m2 per yr and a night respiration of 163 g C per m2 per yr resulting in an annual net carbon available for export or to the benthos of 113 g C per m2 per yr. *** DIRECT SUPPORT *** A01BY015 00002

ANTHROPOGENIC ENRICHMENT AND NUTRIENTS IN SOME TROPICAL LAGOONS OF GHANA, WEST AFRICA

As part of a larger study of demographic change in coastal Ghana, we measured the concentrations of major plant nutrients and phytoplankton chlorophyll in eight coastal lagoons with different land use and human population density. The purpose of our study was to relate human activities to water quality in coastal receiving waters. We also carried out preliminary measurements of stable nitrogen isotopes to quantify the contribution of sewage and fertilizer to fish production in the lagoons. Annual mean concentrations of ammonia, nitrite plus nitrate, dissolved inorganic phosphate (DIP), and water column chlorophyll a varied by factors of over 1400, 15, 315, and 125, respectively, among the eight small coastal lagoons in the Central and Greater Accra Regions of Ghana. Concentrations of ammonia (mean of ∼1 mmol/L) and phosphate (mean of ∼60 μmol/L) in Korle lagoon, near the capital city of Accra, may be the highest yet reported for an estuarine system. In most of the lagoons, nutrient concentrations throughout the study period were much lower than previously reported, perhaps due to analytical problems in earlier measurements. Dissolved inorganic nutrients varied markedly over the year but showed no evidence of a regular seasonal cycle such as commonly observed in temperate coastal systems. Nutrient concentrations did increase sharply and briefly in many lagoons during the wet season. Water column chlorophyll increased greatly during August and September. Since water column inorganic nutrients were very low during July, it is possible that the apparent bloom was stimulated by nutrients brought into the lagoons during coastal upwelling or that the elevated chlorophyll was itself brought into the lagoons from offshore. Human population densities in the watersheds of the lagoons were high and varied widely, from ∼150 individuals/km2 to almost 3300 individuals/km2. Ratios of watershed area to open lagoon area ranged from ∼30 to almost 2500, much higher than is common in most well-studied estuaries and lagoons in the United States. We found a strong correlation between human population density and mean annual dissolved inorganic nitrogen (DIN) concentrations among the wide range of systems studied. Mean annual DIN concentrations in the Ghana lagoons were higher than found in a number of temperate lagoons with similar population density. The relationship between population density and DIP and chlorophyll was weak. The latter may be due to toxic effects in Korle lagoon and abundant filter feeders in another lagoon. Stable nitrogen isotope ratios in two species of fish, a shrimp, and a crab varied consistently among the lagoons, with higher δ15N values indicative of human sewage in lagoons downstream of more densely populated watersheds.

Impacts of different forms of nutrients on the roles of coastal lagoons as nutrient sources or sinks — A mesocosm study

Abstract An experiment was conducted to quantify the effects of enrichment with dissolved inorganic nutrients on the Nand P mass balances of coastal lagoons. The experiment was conducted during summer using mesocosms designed as living models of the shallow coastal lagoons of Rhode Island, USA. The experiment involved five treatments, each conducted in duplicate. Two mesocosms served as controls, and remained unenriched. Two mesocosms were enriched with phosphate alone, two with nitrate alone, two with nitrate plus phosphate, and two with ammonium plus phosphate. The unenriched controls functioned as small sources of Nand P. The mesocosms enriched with phosphate alone showed net releases of N (as in the controls), but a small net retention of P. The inverse pattern applied in the mesocosms enriched with nitrate alone. The mesocosms enriched with N plus P showed net retention of both elements. For both nutrients, the percent retention of the nutrients added to the system was small (ca. 20%), and in the sam...