Kenneth A. Moore

Seasonal pulses of turbidity and their relations to eelgrass (Zostera marina L.) survival in an estuary

The light environment of one Chesapeake Bay tributary where seagrasses have decreased in abundance was described using both continuous and discrete measures of irradiance and related to the growth and survival of transplanted eelgrass (Zostera marina L.). After 8 months of continuous growth at an upriver site, a decline and eventual complete loss of eelgrass transplants began during a month long (May–June) period of increased turbidity (Kd>3.0). Transplant loss continued even after light conditions improved (Kd<2.0). At a downriver site where there has been some natural seagrass regrowth, the pulse of high turbidity was not as evident and transplants survived. Other than this spring period of high turbidity at the upriver site, the light environments of the two areas were similar with minimum turbidity in January and maximum in the spring and summer. Annual median daily attenuation coefficients (Kd) at the upriver and downriver sites were 1.77 and 1.96, respectively, and were not significantly different (P=0.49). Total downwelling quantum flux at transplant depths of 0.8 m below mean sea level were 2618 and 2556 mol·m−2·yr−1, or approximately 24.9 and 24.3% of annual solar PAR. The high spring turbidity pulse corresponded to an increase in non-chlorophyll particulate matter. Chlorophyll specific attenuation (Kc) accounted for 6.7–9.0% of Kd in June. Differences in attenuation were greatest in the 400–500 nm spectral region. Therefore, measures of total PAR attenuation can overestimate the usable irradiance available to the macrophytes. Scalar quantum fluxes during the period of elevated turbidity were 2.7 and 13.4 mols·m−2·day−1 at the upriver and downriver sites. The duration and intensity of total PAR measured upriver during this period were insufficient to support eelgrass growth and survival, and below literature estimates for eelgrass community light compensation at in situ temperatures (20–25°C). Therefore late spring, month-long pulses in turbidity, such as measured here can account for the loss of transplanted vegetation and, potentially, explain lack of successful recruitment into formerly vegetated upriver sites.

Environmental regulation of seed germination in Zostera marina L. (eelgrass) in Chesapeake Bay: effects of light, oxygen and sediment burial

Abstract The effects of light, oxygen and sediment burial on seed germination of Zostera marina L. were tested in two experiments beginning in 1987 and 1988. In 1987, seeds were placed in flow-through clear plastic tubes or buried at depths of 5, 15 and 25 mm in pots filled with seagrass sediments and held in an outdoor running seawater tank at ambient temperature, salinity and solar irradiance. The seeds began germinating in the sediments when water temperatures dropped to 15°C in mid-October and nearly all were germinated by December. Seeds held in the plastic tubes did not begin to germinate until mid-January. Again in 1988, seeds planted in pots germinated in October when temperatures decreased to 15°C; germination in the oxygenated water column was again delayed throughout the autumn and winter. However, seeds held in the water column in clear vials of deoxygenated water, without sediment, displayed a pattern of rapid fall germination identical to that of the sediment treatments. No consistent effect of light and dark treatments was observed in the water-column seeds. We conclude that eelgrass seeds are well adapted for germination in anoxic conditions and that seed germination in this region is keyed to not only seasonal temperature changes, but also oxygen availability.

Analysis of the Abundance of Submersed Aquatic Vegetation Communities in the Chesapeake Bay

A procedure was developed using aboveground field biomass measurements of Chesapeake Bay submersed aquatic vegetation (SAV), yearly species identification surveys, annual photographic mapping at 1∶24,000 scale, and geographic information system (GIS) analyses to determine the SAV community type, biomass, and area of each mapped SAV bed in the bay and its tidal tributaries for the period of 1985 through 1996. Using species identifications provided through over 10,000 SAV ground survey observations, the 17 most abundant SAV species found in the bay were clustered into four species associations: ZOSTERA, RUPPIA, POTAMOGETON, and FRESHWATER MIXED. Monthly aboveground biomass values were then assigned to each bed or bed section based upon monthly biomass models developed for each community. High salinity communities (ZOSTERA) were found to dominate total bay SAV aboveground biomass during winter, spring, and summer. Lower salinity communities (RUPPIA, POTAMOGETON, and FRESHWATER MIXED) dominated in the fall. In 1996, total bay SAV standing stock was nearly 22,800 metric tons at annual maximum biomass in July encompassing an area of approximately 25,670 hectares. Minimum biomass in December and January of that year was less than 5,000 metric tons. SAV annual maximum biomass increased baywide from lows of less than 15,000 metric tons in 1985 and 1986 to nearly 25,000 metric tons during the 1991 to 1993 period, while area increased from approximately 20,000 to nearly 30,000 hectares during that same period. Year-to-year comparisons of maximum annual community abundance from 1985 to 1996 indicated that regrowth of SAV in the Chesapeake Bay from 1985–1993 occurred principally in the ZOSTERA community, with 85% of the baywide increase in biomass and 71% of the increase in are a occurring in that community. Maximum biomass of FRESHWATER MIXED SAV beds also increased from a low of 3,200 metric tons in 1985 to a high of 6,650 metric tons in 1993, while maximum biomass of both RUPPIA and POTAMOGETON beds fluctuated between 2,450 and 4,600 metric tons and 60 and 600 metric tons, respectively, during that same period with net declines of 7% and 43%, respectively, between 1985 and 1996. During the July period of annual, baywide, maximum SAV biomass, SAV beds in the Chesapeake Bay typically averaged approximately 0.86 metric tons of aboveground dry mass per hectare of bed area.

Environmental Factors Affecting Recent Summertime Eelgrass Diebacks in the Lower Chesapeake Bay: Implications for Long-term Persistence

Abstract We investigated the effects of several environmental factors on eelgrass abundance before, during, and after widespread eelgrass diebacks during the unusually hot summer of 2005 in the Chesapeake Bay National Estuarine Research Reserve in Virginia. Systematic sampling with fixed transects was used to investigate changes in eelgrass abundance at downriver and upriver regions of the York River Estuary. Concurrently, continuous and discreet measurements of water quality were made at fixed stations in each area within the eelgrass beds from 2004 through 2006. Results indicate nearly complete eelgrass vegetative dieback during the July–August period of 2005, in contrast to the more seasonal and typical declines in the summer of 2004. Losses were greatest in the deeper areas of the beds and at the upriver site where light availabilities were lowest. Recovery of eelgrass during 2006 was greater in the downriver area, especially at mid-bed depths. By the fall of 2006, no shoot vegetation remained at the upriver site. In 2005, the frequency and duration of water temperatures exceeding 30°C were significantly greater than that of 2004 and 2006. Additionally, the frequencies of low dissolved oxygen excursions of 1–3 mg L−1 during this period were greater in 2005 than 2004 or 2006. These results suggest that eelgrass populations in this estuary are growing near their physiological tolerances. Therefore, the combined effects of short-term exposures to very high summer temperatures, compounded by reduced oxygen and light conditions, may lead to long-term declines of this species from this system.

Distribution of Zostera marina L. and Ruppia maritima L. sensu lato along depth gradients in the lower Chesapeake Bay, U.S.A.

Seventeen transects in areas containing beds of submerged aquatic vegetation in the lower Chesapeake Bay were selected for analysis of the depth distribution of Ruppia maritima L. sensu lato and Zostera marina L. during a 6-week period (25 July–12 September 1978). Transects studied ranged in length from 130 to 1100 m with estimates of percent cover made on 785 plots. Mean importance value (relative frequency + relative cover) for Z. marina was 96.0 (range of 0–200) while for R. maritima it was 94.9 (0–184.4). Average cover across the beds ranged from 0 to 51.7% for Z. marina and 0–79.2% for R. maritima, with average transect biomass up to 72.9 and 55.4 g dry weight m−2 for the two species, respectively. Comparison of individual transects showed a consistent pattern of zonation where R. maritima occupied the nearshore, shallower area which graded to a mixed zone of R. maritima and Z. marina at intermediate depths. At the deepest part of the beds, Z. marina was the only species found. Transects along the western shore sites were characterized by lower percent cover with more open areas in the beds when compared with the eastern shore sites. Depth distributions of R. maritima and Z. marina on the eastern shore were +20 to −100 cm and −30 to −150 cm (mean low water (MLW)), respectively, while on the western shore they were +10 to −80 cm and +10 to −110 cm, respectively. The greater depth penetration of the two species along the eastern shore transect sites may reflect a greater influence of clearer, oceanic water compared with the more turbid, riverine influence along the western shore sites. Results demonstrate that both optimum and maximum depth limits for a species can vary considerably within a particular region and suggest the potential for marked variability over time.

BARNEGAT BAY–LITTLE EGG HARBOR ESTUARY: CASE STUDY OF A HIGHLY EUTROPHIC COASTAL BAY SYSTEM

The Barnegat Bay-Little Egg Harbor Estuary is classified here as a highly eutrophic estuary based on application of the National Oceanic and Atmospheric Administrations National Estuarine Eutrophication Assessment model. Because it is shallow, poorly flushed, and bordered by highly developed watershed areas, the estuary is particularly susceptible to the effects of nutrient loading. Most of this load (;50%) is from surface water inflow, but substantial fractions also originate from atmospheric deposition (;39%), and direct groundwater discharges (;11%). No point source inputs of nutrients exist in the Barnegat Bay watershed. Since 1980, all treated wastewater from the Ocean County Utilities Authoritys regional wastewater treatment system has been discharged 1.6 km offshore in the Atlantic Ocean. Eutrophy causes problems in this system, including excessive micro- and macroalgal growth, harmful algal blooms, altered benthic invertebrate communities, impacted harvestable fisheries, and loss of essential habitat (i.e., seagrass and shellfish beds). Similar problems are evident in other shallow lagoonal estuaries of the Mid-Atlantic and South Atlantic regions. To effectively address nutrient enrichment problems in the Barnegat Bay- Little Egg Harbor Estuary, it is important to determine the nutrient loading levels that produce observable impacts in the system. It is also vital to continually monitor and assess priority indicators of water quality change and estuarine health. In addition, the application of a new generation of innovative models using web-based tools (e.g., NLOAD) will enable researchers and decision-makers to more successfully manage nutrient loads from the watershed. Finally, the implementation of storm water retrofit projects should have beneficial effects on the system.

Interactive effects of light and salinity stress on the growth, reproduction, and photosynthetic capabilities of Vallisneria americana (wild celery)

The effects of light and salinity onVallisneria americana (wild celery) were studied in outdoor mesocosms for an entire growing season. Morphology, production, photosynthesis, and reproductive output were monitored from sprouting of winter buds to plant senescence and subsequent winter bud formation under four salinity (0, 5, 10, and 15 psu) and three light (2%, 8%, and 28% of surface irradiance) regines. Chlorophylla fluorescence was used to examine photochemical efficiency and relative electron transport rate. High salinity and low light each stunted plant growth and reproduction. Production (biomass, rosette production, and leaf area index) was affected more by salinity than by light, apparently because of morphological plasticity (increased leaf length and width), increased photosynthetic efficiency, and increased chlorophyll concentrations under low light. Relative maximum electron transport rate (ETRmax) was highest in the 28% light treatment, indicating increased photosynthetic capacity. ETRmax was not related to salinity, suggesting that the detrimental effects of salinity on production were through decreased photochemical efficiency and not decreased photosynthetic capacity. Light and salinity effects were interactive for measures of production, with negative salinity effects most apparent under high light conditions, and light effects found primarily at low salinity levels. For most production and morphology parameters, high light ameliorated salinity stress to a limited degree, but only between the 0 and 5 psu regimes. Growth was generally minimal in all of the 10 and 15 psu treatments, regardless of light level. Growth was also greatly reduced at 2% and 8% light. Flowering and winter bud production were impaired at 10 and 15 psu and at 2% and 8% light. Light requirements at 5 psu may be approximately 50% higher than at 0 psu. Because of the interaction between salinity and light requirements for growth, effective management of SAV requires that growth requirements incorporate the effects of combined stressors.

Growth of Zostera marina L. Seedlings under laboratory conditions of nutrient enrichment

Abstract The effect of increased nutrients on growth of Zostera marina L. seedlings was tested in the laboratory by adding 2 different formulations (18:6:12 and 14:14:14 Nitrogen: Phosphorus:Potassium (N:P:K), respectively) of a slow release fertilizer, Osmocote®. Three different application rates were used with the 2 formulations by placing appropriate amounts in peat pots containing 1 seedling each. The addition of fertilizer to the substrate markedly stimulated the growth of seedlings. Nutrient enrichment promoted growth both in terms of increased leaf length and vegetative production of shoots. The nitrogen rich formulation (18:6:12) produced less growth than the equal balance formulation (14:14:14). For both formulations, the highest concentrations produced greater growth than other concentrations of the same formulation. At equal application rates with respect to nitrogen, less growth occurred in the treatments receiving less phosphorus. Results of this experiment corroborate results from previous work suggesting that addition of nutrients to the sediment can stimulate Z. marina growth.

Zostera marina L. growth response to atrazine in root-rhizome and whole plant exposure experiments

Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino-]-s-triazine), a triazine herbicide, is one of the most widely used herbicides in the Chesapeake Bay watershed. Increased use of atrazine in the 1970s coincided with a decline in the abundance of Zostera marina L. (eelgrass). Ground-water surveys have found atrazine in concentrations that may affect eelgrass growth and survival. The effects of atrazine in groundwater discharges on the growth of eelgrass through root-rhizome exposure were examined in laboratory systems. A long term, dynamic, groundwater simulation study was conducted with atrazine concentrations ranging from 0.0 to 2.5 mg·l−1. No significant effects on chlorophyll content, growth or survival were detected. A static root-rhizome exposure experiment was conducted using split chamber exposure systems to verify these results, atrazine concentrations were increased by an order of magnitude. Neither mortality nor significant effects on plant growth were detected (maximum atrazine concentration 7.6 mg·l−1). A static, whole plant exposure experiment was conducted, and mortality was observed at atrazine concentrations of 1.9 mg·l−1 and above. This work suggests that eelgrass is not susceptible to atrazine through root-rhizome uptake, and that atrazine exposure via groundwater seepage did not cause the declines in eelgrass abundance and distribution.

The Biology and Propagation of Zostera marina, Eelgrass, in the Chesapeake Bay, Virginia

Seasonal aspects of the standing crop of Zostera marina leaves and roots and rhizomes, leaf length and shoot density were measured at five sites in three locations in the lower Chesapeake Bay: one site at Browns Bay in the Mobjack Bay and two sites each at the Guinea Marshes located at the mouth of the York River and Vaucluse Shores located on the Eastern Shore. Sampling at most sites occurred from June 1978 to July 1980. Shoot density, mean leaf length and total standing crop of Ruppia maritima were also obtained at one of the Vaucluse Shores sites and at the Browns Bay site. The standing crop of Zostera marina vegetative shoots increased in the spring of each year and was hightest in the June-July period at all sites. Minimal values for standing crop occurred during the fall-winter period in both years. Differences in standing crop were found between years ·for similar time periods at each site. Root-rhizome standing crop followed similar trends as the shoot standing crop. Reproductive shoots made up less than 25% of the total number of shoots during the spring period when they were present. Lowest density of shoots occurred in the late summer and early fall while highest density occurred in the spring and early sununer months although there was some variation at several of the sites. Growth of Zostera marina appeared to occur primarily from late September to early July as temperatures ranged from 0°C to 25°C. Almost no growth occurred in late July, August or early September when no new shoots were observed and when water temperatures exceeded 25°C. Comparison of these data with data collected from sites along the East Coast of the U.S. indicated similarities in the growth cycles at all sites except that maximum standing crop measurements were attained earlier in more southern areas and later in more northern locations. Temperature appeared to control growth although results from recent studies indicate that irradiance is also critical in determining timing of leaf growth. Rupia maritima also exhibited distinct trends in seasonal standing stock measurements. Growth patterns were similar to Zostera marina except that maximum values occurred later in the sununer while minimal values were obtained in March. The reproductive phase also occurred in the sunnner after Z. marina had been completed.