Part II - SUMMARY OF COMPLETED PROJECT
Understanding the dynamics of ecosystem state change, including both the transitions among ecosystem states and succession within these states is the research theme of the Virginia Coast Reserve Long-term Ecological Research (VCR LTER) project. The Virginia Coast Reserve is an extremely dynamic, frequently disturbed landscape which is comprosed of elements (e.g., marsh, grassland, forest) that differ in degrees normally associated with biome-level differences. The central hypothesis of the VCR LTER is that ecosystem, landscape and successional patterns are controlled by the relative vertical positions of the land, sea, and fresh-water table. Specific accomplishments include establishment of long-term experiments which manipulate land, sea and fresh-water surfaces, dating of landscapes and historical reconstructions of past landscapes, development of models and new theories of ecosystem state change, lagoon dynamics and marsh-upland transitions and development of long-term datasets in the areas of disturbance, primary productivity, trophic structure, soil organic matter, and nutrient movements.
Part III - TECHNICAL INFORMATION
Our studies are conducted at the Virginia Coast Reserve (VCR) on Virginia's Eastern Shore. The Nature Conservancy is the steward of our site. During the two years of LTER II, we extended our research from LTER I, continued our systematic long-term measurement program, initiated three long-term experiments designed to bring about transitions in ecosystem states, incorporated new technologies needed to obtain high resolution measurement of critical landscape attributes (sea, land, and water table levels), and further developed our research infrastructure in support of long-term research.
From January 1992 through the present, 31 journal articles have appeared in print,14 are in press (1994 citations) and 13 are under review (1994 citations). VCR PIs have contributed 15 book chapters in print and 4 in press and 2 books which offer synthesis of research and theory at the site and also support intersite and network initiatives. Twelve theses and dissertations were completed.
This document summarizes our scientific activities for each of the 4 main research sites at the VCR: 1) The VCR Megasite; 2) The North Hog Chronosequence Site; 3) The Mainland Marsh Site; and 4) The Hog Island Bay Lagoons and Marshes Site. In addition, we review the progress of our long-term experiments; detail our accomplishments resulting from intersite, network, modeling and synthetic studies; and identify the relationship between past and proposed work.
Large-scale, long-term research at the VCR focuses on the causes and effects of ecosystem disturbance and change. For example, we detailed the hydrodynamics of the greatest coastal storm since 1942 (Davis and Dolan 1992); we derived estimates of the wave energies of 1447 coastal storms since 1942 (Dolan and Davis 1993) and analyzed the impact of these storms on island dynamics (Fenster and Dolan 1994). We calculated the occurrence probabilities of 100 barrier island plant species across the historical storm disturbance gradient (Fahrig et al 1993). We have also documented, using tree rings, individual tree response to hurricanes (Johnson & Young 1992). On longer time scales Foyle (1994), Foyle and Oertel (1994), Oertel and Kraft (1993) and Oertel et al. (1993) charted the drainage patterns of VCR lagoons and showed their continuity with paleochannels on the continental shelf. These finding stimulated a new model for the origin of the lagoon and marshes of mid-Atlantic barrier islands (Oertel and Kraft 1993).
Recent efforts include increased use of remotely sensed data as a tool for documenting ecosystem processes. We completed the GIS framework for the annual VCR colonial bird nesting survey and have included the 1993 GPS geo-referenced bird survey is in this system. In the long-term we will track changes in utilization of the landscape by colonial birds. In addition, we have mapped land cover and changes in land cover for the VCR using TM satellite imagery. We installed a NASA sun photometer to better correct satellite imagery for atmospheric effects; completed our first study of spectral reflectance of barrier island plants (Carter and Young 1993); and demonstrated the utility of TM, Spot and aerial photography for analysis for vegetation change (Porter and Callahan 1994).
Habitat composition and utilization at this large spatial scale remain strong research areas. Biogeographic surveys of island vegetation, lagoonal fish (Yozzo 1994), marcoalgae (Monti 1993), formainifera (Woo 1992), and insular small mammal populations (Porter and Dueser 1994, Scott and Dueser 1992, Halama and Dueser 1992) were completed in late 1993. Tissue samples were collected for allozyme analysis of small mammals on 11 islands; analysis of blood samples to test for the presence of Hantavirus were negative (Moncrief, pers. comm.). Forys and Dueser (1993) documented movements of rice rats (Oryzomys palustris) between Crescent and Parramore Islands, all of which originated on the smaller island. We found that rats dispersing between islands comprise a statistically random subset of the resident population with respect to age and sex, unlike overland dispersers which are predominantly juveniles. Our biogeographic surveys are conducted on a campaign basis, with expected surveys at intervals of 3-5 years.
Harris (1992) identified and dated a chronosequence of dune and swale landscape elements between the ocean and the lagoon behind Hog Island. The youngest features are located near the active beach, and the oldest (dating from ~1871) are adjacent to the lagoon-side marsh (F. Several studies indicate that dune age is an important control on ecological development. For example, soil nitrogen (ammonium and nitrate), net N-mineralization, and total N-mineralization rates are all highest in the oldest terrain and lowest in the newest landscapes (Young et al 1992). Decomposition rates are greater in older landscapes than in newer terrain, and total below ground biomass increases from 582 g/m2 to 3035 g/m2 with increasing age of swales through the 120 year chronosequence. Above ground and below ground production on the dunes decreases with increasing site age; available nitrogen increases with age in the chronosequence while nitrogen mineralization is not well explained by landscape age. Continued chronosequence research will focus on long-term responses of primary production, organic turnover, and nutrient cycling rates to changes in island hydrology, nutrient availability, herbivory and storm events.
Through extensive surveys we have established the relationship between perched freshwater reserves and local land elevation across scales from microtopographic variations on marsh surfaces to the scale of dune/swale systems. In this framework, coastal storms transport sand and elevate land surface levels, thereby permitting higher fresh water-table elevations (Stasavich and Hmieleski 1993). Interestingly, over 90% of the beach sand washed inland by storm events remains in place on the island; only 10% of the sand returns to the beach by winds (Cohn 1993; Clark 1993). In areas of Hog Island where storm overwash disturbance is frequent, clonal growth forms dominate (Fahrig et al. 1993). Both ocean side flooding due to storm surge and lagoon side flooding due to wind tides result in salinity stresses on terrestrial island vegetation. Young and co-workers have studied the effects of salinity on barrier island flora. Young et al. (1994) established the salitinty tolerances of individual plant species. Johnson & Young (1992) determined the sensitivity of pines to salt water flooding and the effects of pore-water salinity on germination (Sande & Young 1992) and primary productivity (Young 1992). These studies highlight the sensitivity of the VCR ecosystem to subtle changes in the relative elevations of the land surface and the fresh/salt water interface.
Our studies of marsh dynamics at the landscape level have lead us to propose a conceptual model of sea-level induced transition from terrestrial forest to estuary (Brinson et al. 1994). Important components of this model include self-maintaining properties and state changes due to disturbance or exposure to acute stress. The mechanisms responsible for maintenance and transition along the gradient from lagoon to upland are unique for each zone within the marsh. For example, the position of the upland-high marsh transition depends upon the slope of the marsh surface and the distance from a tidal creek. Along steep marsh surface slopes, elevation is the primary factor influencing the position of the transition, while along very gentle slopes distance from the nearest tidal creek is most important.
Along the gradient from low to high marsh at the mainland marsh site, root decay processes apparently are not affected by sediment physico-chemical differences, although root production is much greater in the mid-marsh zone perhaps due to tidal inundation conditions. Greater root production and slower root turnover occur in the mid-marsh sediments with highly variable salinities, high oxidation-reduction potentials, lower sediment saturation, and high sulfide concentrations. Differences in organic matter accumulation between high and low marsh areas are thus due to differences in root production rather than root decomposition (Blum 1993). Although position in the marsh and sediment pore water chemistry has little effect on root decay, Juncus roots decay two times faster than Spartina roots. This difference is consistent with the difference in the starting C:N ratios of 37:1 and 47:1 for Juncus and Spartina, respectively. We are comparing two methods for measuring below ground decay: (1) decay in undisturbed plots in which new organic matter production is prevented by removing above ground plant material and pruning roots to exclude new root growth, and (2) decay in buried litter bags -- and conclude that regardless of the type of organic matter (i.e., Juncus or Spartina) or location in the marsh, the vast majority of below ground organic matter is old and recalcitrant (Christian et al. 1993) and/or the removal of new below ground root material restricts decomposition (Tirrell and Blum 1992).
Field measurements and GIS analysis of aerial photography were used to correlate landscape evolution to sedimentary processes at the Mainland Marsh Site. The marsh area has increased by 8% over 50 years, primarily because of upland encroachment (Kastler 1993). Lead dating of the sediments indicate a sediment accretion rate of 2 mm per year (Kastler 1993), which is consistent with earlier measures by Barr (1989) and Oertel (1992). Analysis of the clay mineralogy of marsh sediments indicate that this marsh developed on top of upland soils similar to those found in neighboring agricultural and forested areas (Robinson 1993).
At the Mainland Marsh Site and in other VCR tidal creeks, the rate of carbon cycling by bacteria is much lower than in nearby creeks of Chesapeake Bay despite high concentrations of inorganic N and P (MacMillin et al. 1992). The high inorganic nutrient pools combined with the low levels of bacterial productivity indicate that bacterial production is not limited by N or P and that the amount of carbon moving through the bacterial loop is low relative to Chesapeake Bay tidal creeks on the Delmarva Peninsula. Comparative studies of VCR marshes and tidal creeks with those of Chesapeake Bay will continue through funding from NOAA Sea Grant program. The Phillips Creek area in the Mainland Marsh Site will continue to be a focal point for research into the processes that govern the hydrology, geochemistry and ecology of the marsh system.
Textural and mineralogical analysis of inorganic sediments from throughout the VCR revealed that each physiographic area (i.e., mainland, marsh surface, channel bottom) has a distinct sedimentological signature (Oura 1993; Robinson 1993). Regions of elevated paleotopography are identified as drowned uplands through the presence of kaolinite and vermiculite (similar to mainland soils) sampled in meter-deep cores. Preliminary 210Pb dating of sediment cores suggests that sedimentation rates in the VCR system are 1.0-2.2 mm/yr (Kastler 1993); major storm horizons are easily identified within the shallow cores (Kastler 1993; Robinson 1993).
Sediment texture places important constraints on the productivity of individual marsh plants. For example, sandy creek-bank areas that are flushed by semi-diurnal tides are highly productive; in contrast, sandy areas that are not subject to twice daily inundation achieve hypersaline conditions and have low Spartina alterniflora productivity (Robinson 1993). In addition, Hussey and Odum (1992) found substantial differences in marsh evapotranspiration (ET) across salinity gradients; the highest ET and LAI are measured in marshes with low salinity, suggesting that above ground primary production is salinity dependent. Extractable ammonium and porewater ammonium and phosphate in the surface layers of young salt marshes (10-13 years) are nearly identical to those in marshes >100 years old, indicating a more rapid chemical maturation than previously determined (Osgood and Zieman 1993a,b; 1994).
| Variable(Exp. Site) | Method | Resolution | Frequency |
|---|---|---|---|
| Land Surface Elevation1, 2, 3 | Laser Total Station | 1 mm | Biannual |
| Fresh-water Table Elevation1, 3 | Pressure Transducer | 1 cm | Hourly |
| Tides & Inundation Freq & Ht1, 2, 3 | Pressure Transducer | 1 cm | 6 min. |
| Decomposition1, 2, 3 | Wooden Dowels Mass Loss | 0.1 g yr-1 | Annual |
| Aboveground Primary Prod1, 2, 3 | Maximum Biomass | 10 g m-2 yr-1 | Annual |
| Organic Matter Accumulation1, 2, 3 | Belowground Litter Bags | 1 mm | Annual |
| Sp. Comp., Density & Biomass 1, 2, 3 | 0.25 m2 quadrat, Count, Weight | count, 0.1 g yr-1 | Annual |
| Sediment Deposition2, 3 | Settlement Plates | gm m-2 | Quarterly |
| Bulk Density2, 3 | Cores Dry Wt. | 0.1 g cm-3 | Annual |
| Evapotranspiration1 | Water Table Integration | 1 mm/d | Daily |
| Sediment Erosion & Deposition2, 3 | Sediment Table | 1 mm | Monthly |
| Sediment Organic Matter2, 3 | Loss on Ignition | % | Annual |
| Sediment Organic Matter3 | C:N (Carlo-Erba) | % | Annual |
| Sediment Organic Matter3 | 1mm Macro-OM | gm m-2 | Annual |
| Sediment Redox2, 3 | Platinum Electrode | mV | Quarterly |
| Pore Water Chemistry1, 2, 3 | Salinity (Refractometry) Ammonium (spectrophoto) Phosphate (spectrophoto) H2S(spectrophoto) | ppt <1micromole <1micromole <1micromole | Quarterly Quarterly Quarterly Quarterly |
| Rainfall1, 3 | Tipping Bucket | 5 mm | Continuous |
| Solar Energy1 | Solar Cell | 2 W m-2 | Hourly |
| Water Pumped1, 3 | Flow Meter | 0.1 L hr-1 | Hourly |
| Short-term Denitrification; Nitrification3 | Acetylene Block & 15N-dilution | ng g-1 hr-1 | Quarterly |
| Short-term Trace Gase Evolution3 Sed. Respiration CO2, CH4, and NOx | GC & Chemiluminescence CO2 - O2 exchange | ng m-2 hr-1 | 2x yr-1 |
| Short-term Invert. & Nekton Density3[1] | Quadrats, ID, Count, Weight | individuals | Summer |
| Surface Water Velocities & Drainage Patterns on Ebb and Flood Tides3 | Marsh-McBirney Sontek Acoustic Current Meter | 1 cm s-1 | Biannually + Intensively |
| Bed & Suspended Sed. Characteristics in Ditch, Creeks and Marsh3 | Textural Analysis | 1% | Quarterly |
| Suspended Solids Concentration3 | Optical and Physical | 2 mg l-1 | Intensively |
| Data Type | Period of Record | Number of Stations | Sample Frequency | Comments | Responsible PI |
|---|---|---|---|---|---|
| Weather | 6/88 - | 3 stations | Hourly | LTER III stations, 17 variables | Porter |
| Rainfall | 1835 - 1994 | Ft. Monroe | Daily | Longest benchmark station in area | Porter |
| Tides | 6/88 - | 2 stations | 12 minutes | New stations to be added in 1994 | Porter |
| Wells | 7/89 - | 72 stations | Weekly Strip Chart | Electonic replacements in 1994 depth and salinity recorded | Brinson/Porter |
| Cores | 18,000 yrs | 29 stations | ~ 500 yrs | Long cores, silt, sand clay, forams, shell, and pollen | Oertel
|
| 200 yrs | 41 stations | ~ 10-20 yrs | Short cores, silt, sand, clay, shell | Kochel | |
| Vegetation | 8/89 - | 2x(23 5x5m plots) | 5 yrs | Plots are on 2 transects across Hog Island. | Young Day Shugart |
| Root Phenology | 5/91 - | 1 station | Seasonally | Station on the Hog Island Chronosequence Dune | Day |
| Lidet Data | 5/91 - | 3 stations | Yearly | Part of LTER Intersite Study | Blum |
| Productivity | 6/88 - | 2 stations | Yearly | Spartina on Hog Island Spartina on other marshes | Zieman Blum |
| 6/88 - | 4 stations | Yearly | Myrica on Hog Island | Young | |
| Bacteria | 6/88 - | 10 stations | Monthly | Phillips Creek and Hog Island Abundance, growth & activity. | Blum |
| Forests | 2/93 - | 100 stations | 5 yrs | Paramore Island for FORET | Shugart |
| OM Survey | 5/88 - | 35 stations | 5 yrs | Top 10 cm samples on each major vegetation type. % OM | Blum |
| Mammals | 8/88- | 4 transects | 6 mo. | Census of small mammals | Porter & Dueser |
| 1974 - | All Islands | 5-10 yrs | Extensive surveys small mammals | Porter & Dueser | |
| Birds | 1975 - | Marshes Shoreline | Yearly | Va. Dept. Game and Inland Fisheries, TNC | Porter |
| Water Qual. | 1/91 - | 10 stations | Monthly | Temp. salinity, light extinction, NH4, PO4, TSS POM, O2 NO3, NO2, BOD, Chl-a | Blum |
| Wet/Dry Deposition | 1/91 - | 1 station | Continuous | Part of a regional data collection program of Galloway. Hog Island. | Galloway |
| Aerial Photographs | 1949 - | Megasite | ~ 8 yrs; now ~1 - 2yrs | Provided by or purchased from Federal and State agencies. 239 sets available | Hayden |
| Satellite Images | 1989 - | Megasite | Irregular | 2 Spot Images 2 TM Images | Porter |
| Waves | 1942 - | Megasite | Every storm | Wave height data on 1,475 storms | Hayden |
| 1960 - 1988 | 8 stations | Monthly | CalculatedWave heights and periods, USACE | Hayden | |
| 1962 - | 1 station | Daily | VA Fisheries | Hayden | |
| Storms | 1885 - | 4 stations | Monthly | Monthly frequencies tabulated | Hayden |
| Erosion | 1949 - | every 50 m | ~ 8 yrs | Shorelines of all islands included | Hayden |
| Veg. Line | 1949- | every 50 m | ~ 8 yrs | Strand veg. for all islands | Hayden |
| Storm Surge | 1899 - | 1 station | Monthly | Model generated data. | Hayden |
| Climate | 1836 - | 19 stations | Daily | Class B Stations of the NWS station records vary in length | Hayden |
| Waterfowl | 1967 - | VCR | Yearly | The Nature Conservancy | Truitt |
| Peregrine | 1977 - | VCR | Yearly | The Nature Conservancy | Truitt |
| Trace Gas | 1994- | 4 | Seasonal | Network Trace Gas Project | Anderson |
| Isotopic Abundance | 1992-94 1995- | 12 16 | Irregular Seasonal | General Surveys With Trace Gas Nework | Macko |
| Archived Material | Number of Items | Archive Location | PI Responsible |
|---|---|---|---|
| Long Sediment Cores (~ 10,000 yrs) | 50 Cores | Oceanography, ODU | Oertel |
| Short Sediment Cores (~ 1000 yrs) | 67 Cores | Geology, Bucknell Univ. | Kochel |
| Surface Cores (~200 yrs) | 30 Cores | Env. Sci., University of Virginia | Zieman |
| Surface Cores (~100 yrs) | 5 Cores | Env. Sci., University of Virginia | Furman |
| Aerial Photography (1949-1993) | 70 Sets | Env. Sci., University of Virginia | Dolan |
| Thematic Mapper Images | 3 Images | Env. Sci., University of Virginia | Porter |
| Spot Images | 2 Images | Env. Sci., University of Virginia | Porter |
| Mammalian Vouchers | 77 Individuals | Va. Museum Nat. History | Moncrief |
| Mammalian Tissue Samples | 22 Samples | Va. Museum Nat. History | Moncrief |
| Belowground Macro-organic Matter | 100 Samples | Biology, ECU | Christian |
| Litter Bag Organic Matter | 60 Samples | Biology, ECU | Christian |