JEQ Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Related articles in JEQ
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Agricola
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Related Collections
Right arrow Surface Water Quality
Right arrow Biogeochemical Processes
Right arrow Watershed and Landscape Processes
Right arrow Nutrients
Right arrow Nutrient Cycling
Published in J. Environ. Qual. 33:576-580 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORT

Landscape and Watershed Processes

Trophic Transition in a Lake on the Virginia Coastal Plain

Mellisa A. Pensa* and Randolph M. Chambers

Department of Biology, College of William and Mary, Williamsburg, VA 23187

* Corresponding author (mapens{at}wm.edu).

Received for publication May 22, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
To examine possible connections between lake trophic status and runoff from surrounding subwatersheds, we determined patterns of sediment and nutrient deposition in a hypereutrophic, 16-ha impoundment on the Virginia coastal plain. Spatial survey of nutrients in surface sediments documented a strong correlation between total P and extractable Fe (r2 = 0.53). Elevated biogenic silica concentrations up to 0.25% by weight were measured in sections of the lake receiving perennial stream discharge. Sediment C to N ratios were >20 in those same sections, suggesting a large allochthonous contribution to organic matter deposition. Sediment cores 0.9 to 2.3 m in length, representing 70 years of deposition, were analyzed to develop vertical profiles of changes in sediment and nutrient deposition in deltas downstream from two more-developed and three less-developed subwatersheds (with 49 and 9% commercial and residential development, respectively). The average sediment weight percent ± standard deviation of biogenic silica (0.027 ± 0.037 vs. 0.009 ± 0.006%) and total P (0.040 ± 0.025 vs. 0.024 ± 0.019%) was significantly higher downstream of more-developed subwatersheds. Using elevated P loadings and biogenic silica deposition as proxies for algal production, transition of the lake to its current hypereutrophic state appears to have occurred in the last 70 yr. Changes in trophic status as revealed by sediment analysis of this small lake on the Virginia coastal plain reflect a common pattern of eutrophication observed for the entire Chesapeake Bay drainage basin. Analysis of sediments from stream deltas appears to be a reasonable strategy for identifying and targeting subwatershed areas needing better management of nutrient runoff that otherwise would lead to eutrophication of downstream waters.

Abbreviations: BSi, biogenic silica


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
NATIONWIDE, MANMADE CONSTRUCTION of approximately 2.6 million small impoundments has fundamentally changed the patterns of flow through U.S. watersheds (Smith et al., 2002). Water and associated materials are detained or retained for long periods in these new landscape elements, instead of being transported downstream over shorter time scales. Further, with ongoing development, upland ecosystems release more sediment and other materials that discharge into these small freshwater bodies and lead to dramatic changes in trophic structure. Allochthonous inputs of organic matter and inorganic nutrients hasten eutrophication via accumulation of both recycled and new production (Caraco et al., 1992; Granéli, 1999). Owing to rapid infilling, the ephemeral nature of small impoundments makes them potentially important sinks for sediment, organic matter, and inorganic nutrients that otherwise would be carried downstream to estuarine and coastal waters.

Increased nutrient inputs to lakes typically stimulate algal production and eutrophication (Kenney et al., 2002; Verschuren et al., 2002). The dominance of one class of algae—the diatoms—is dictated largely by P and silica availability (Brady and Brugam, 2002). Increased P loading leads to greater diatom production, which causes an accumulation of biogenic silica (BSi) in the sediments (Conley et al., 1993). Biogenic silica concentration serves as an indicator of diatom productivity, and therefore overall phytoplankton efficiency (Peinerud et al., 2001). Recently, Colman and Bratton (2003) determined that increased BSi concentrations in Chesapeake Bay sediments were associated with human impacts in the surrounding watershed. Biogenic silica accumulation often is used as a proxy for nutrient loading and algal production in aquatic systems.

Human development and modification of Virginia open space has accelerated dramatically in the last 50 yr (Southern Environmental Law Center, 2002). Our objective for this study was to determine the effects of changing land use on the nutrient status of a small impoundment on the coastal plain of Virginia, located in the Chesapeake Bay drainage basin. We documented the spatial distribution of nutrients and organic matter in the lake, for comparison with the historical sedimentation of materials in the deltaic environments of perennial streams discharging to the lake. The accumulation of P and BSi was used to infer changes in nutrient availability, algal production, and lake eutrophication.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Study Site
Lake Matoaka is an impoundment located on the southeastern coastal plain in Williamsburg, VA (Fig. 1) . The lake originally was a small millpond created sometime between 1720 and 1730 by damming a riparian-forested wetland in the College Creek drainage basin. In 1930, the height of the spillway was raised about 1 m and the lake area increased to its current size of 16 ha. The College of William and Mary, private housing, and commercial development have cleared part of the 600-ha watershed surrounding Lake Matoaka to the north and east. Two perennial streams (College Creek and Crim Dell Creek) discharge into Lake Matoaka from the north and east, respectively (Fig. 1). In contrast, three smaller, perennial streams discharge into Lake Matoaka from the western portion of the watershed dominated by second-growth oak (Quercus spp.)–hickory (Carya spp.) forest. Based on poor water quality, the lake currently is described as hypereutrophic (Rhodes et al., 1993).



View larger version (19K):
[in this window]
[in a new window]
  		Fig. 1. Outline of the Lake Matoaka watershed in southeastern Virginia, showing the location of five perennial streams (solid lines) and associated subwatersheds (dotted lines). Subwatershed coring stations in the five stream deltas in the lake are shown.

 
Sediment Collection
All sediments for the current study were collected between April and June 2002. To determine the lake-wide, spatial variation in sediment characteristics, we used a spear-corer with a 20-mm-diameter polycarbonate pipe to collect duplicate samples of surface sediments from 50 locations around the lake. Each sampling point was georeferenced using a global positioning system (GPS) with post-processing differential correction. From each core, the upper 3 to 4 cm of sediment were extruded into a 20-mL glass vial, capped, and frozen for later processing.

To determine the historical variation in sediment characteristics, we collected long cores from the aggraded deltas of the five perennial streams discharging into Lake Matoaka (Fig. 1). At each location, a backpack-mounted vibracorer was used to push a 7.5-cm-diameter aluminum-coring pipe into the sediment until resistance. The delta cores were capped and transported to the lab, where they were split open longitudinally. Sediment horizons in the cores were distinguished using a Munsell soil chart, placed in separate sealed plastic bags, and frozen for later processing.

Sediment Analysis
All frozen surface sediments and delta sediments were lyophilized and homogenized with a mortar and pestle before analysis. Organic matter was determined as weight loss on ignition at 450°C of a pre-weighed, dried sediment sample. The remaining ash was resuspended in 0.2 M HCl with heating for 1 h at 80°C, then the extract was analyzed for total dissolved P using the ascorbate-molybdate technique (Parsons et al., 1984) and for extractable Fe using the ferrozine technique (Stookey, 1970). Elemental C and N content was determined for all sediment samples using a Fisons (Beverly, MA) elemental analyzer with accuracy on known sediment standard within 5%.

Biogenic silica analysis was completed using a modification of the method described by DeMaster (1981). A known weight of sediment was extracted in a sodium carbonate solution at 80°C for 5 h, and samples were withdrawn every hour for silica analysis using standard methods (American Public Health Association, 1981). Based on the rapid dissolution of BSi relative to the more gradual release of silica from minerals, the results from the first hour of extraction were used to calculate the total concentration of BSi in sediment samples.

Spatial variation in the environmental quality of surface sediments was plotted using ArcView GIS (ESRI, 1999) to distinguish locations on either side of the median value for extractable Fe, total P, organic matter, and BSi. Historical variation in the characteristics of delta sediments was plotted as depth profiles, and nutrient concentrations were expressed as group averages ± one standard deviation. Where appropriate, relationships between variables were calculated using standard linear regression. Depth-weighted average concentrations of nutrients in delta sediments from the two more-developed subwatersheds and in sediments from the three less-developed subwatersheds were compared using unpaired t tests ({alpha} = 0.05).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Surface Sediments
In Lake Matoaka, the weight percent of reactive Fe concentration averaged 0.14 ± 0.1% and typically was higher in the deepest portion of the lake, with lower values measured in the upper reaches (Fig. 2) . Sediment P concentration averaged 0.083 ± 0.05% and exhibited a distribution pattern strongly similar to reactive Fe. Concentrations of reactive Fe and total P were closely correlated (r2 = 0.53) (Table 1).



View larger version (108K):
[in this window]
[in a new window]
  		Fig. 2. Median separation plots for HCl-extractable Fe (open circles = 0.03–0.14%, filled circles = 0.15–0.40%) and total P (open circles = 0.02–0.12%, filled circles = 0.13–0.30%) in surface sediments of Lake Matoaka.

 

View this table:
[in this window]
[in a new window]
  		Table 1. Correlation matrix of r2 values for linear regressions between variables in surface sediments collected from Lake Matoaka.

 
Organic matter of surface sediments averaged 12.7 ± 5.0% and was lower in the upper reaches nearer stream discharge sites, relative to the central portion of lake (Fig. 3) . Lower organic matter percentage also was measured in surface sediments in the deepest portion of the lake near the outlet. Biogenic silica concentration in surface sediments of Lake Matoaka ranged from less than 0.01 to 0.25% by weight. Most sampling locations in the College Creek arm of the lake had BSi concentration greater than the mean of 0.106 ± 0.06%. Generally, higher concentrations of both organic matter and BSi were measured in the central portions of the eastern arm of the lake, relative to more shallow locations closer to lake margins (Fig. 3).



View larger version (96K):
[in this window]
[in a new window]
  		Fig. 3. Median separation plots for weight percent organic matter (open circles = 5–13%, filled circles = 14–40%) and biogenic silica (open circles = 0.01–0.10%, filled circles = 0.11–0.25%) in surface sediments of Lake Matoaka.

 
The ratio of C to N in surface sediments exhibited a distinct spatial separation between locations with values of <20:1 and ≥20:1 (Fig. 4) . Higher C to N ratios were typical of sediments located in the upper, shallow arms of the lake, whereas lower ratios were measured in deeper portions of the lake away from sites of stream discharge.



View larger version (111K):
[in this window]
[in a new window]
  		Fig. 4. Molar C to N ratios in surface sediments of Lake Matoaka. Open circles = C to N ratio of <20, filled circles = C to N ratio of ≥20. One-meter depth contours are shown; depths of >3 m are shaded darker.

 
The strongest positive correlation between surface sediment variables was observed for C and N (r2 = 0.61) (Table 1). Significant but weaker correlations also were measured between N and P (r2 = 0.16) and between BSi and C (r2 = 0.18).

Delta Sediments
Deposition of sediment since the lake size was expanded in 1930 was identified by the occurrence of a dark, highly compacted organic peat occurring at variable depths in the five cores, from 0.9 to 2.3 m. We associated this peat layer with the soils of the original riparian forest wetland that was flooded in 1930. Sediment analyses were completed on those layers above the peat (i.e., on layers representing fine lacustrine muds and more coarse deltaic silts and sands). No sediment dating was available for these five cores, but from analyses of other cores in Lake Matoaka, Duckworth (1997) determined that sedimentation rate in the College Creek stream delta was 1 to 4 cm yr–1.

Based on profiles from the delta cores collected from Subwatersheds (SW) 1 to 5, BSi concentrations typically were higher from locations downstream of significant upland development (Fig. 5) . For the SW 2 core especially (College Creek), a pattern of increasing BSi concentration in more recently deposited sediments was evident. Silica concentrations were high but less variable from the SW 1 core, and generally lower from the other SW 3 to 5 cores downstream of second-growth forest. Total P was on average higher from cores SW 1 and 2, but there was more overlap in concentration among cores, with no obvious depositional trend by depth (Fig. 5).



View larger version (24K):
[in this window]
[in a new window]
  		Fig. 5. Depth profiles of biogenic silica and total P from delta cores downstream of more-developed Subwatersheds 1 and 2 (solid symbols) and less-developed Subwatersheds 3, 4, and 5 (open symbols).

 
Because of upland commercial and residential development during the past century, only 51% of the land in the two larger, more-developed subwatersheds (SW 1 and 2) currently is second-growth forest, whereas 91% of the land in the three smaller, less-developed subwatersheds (SW 3 to 5) is forest (Table 2). The average concentrations of C and N in delta sediments from these subwatershed types were not significantly different, but BSi was higher from the more-developed SW 1 and 2. Also, as a result of significantly higher P concentration (Table 2), the average ratio of C to N to P was 212:9:1 from delta sediments downstream of SW 1 and 2, and 307:17:1 from sediments downstream of SW 3 to 5.


View this table:
[in this window]
[in a new window]
  		Table 2. Comparison of sediments collected from cores in stream deltas from subwatersheds with different land uses.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
The subwatersheds surrounding Lake Matoaka have experienced different amounts of historical development (Table 2). Since the lake's expansion in 1930, the more-developed subwatersheds appear to have delivered sediments and nutrients that have stimulated algal production in the lake. Runoff from extensive commercial and residential development of SW 1 and 2 is documented by significantly higher concentrations of P and BSi in lake sediments (Fig. 5). It is likely these inputs have contributed to the recent transition of Lake Matoaka to a hypereutrophic system.

The significant positive correlation between P and Fe concentrations in surface sediments of Lake Matoaka supports a common observation in many lakes that inorganic Fe largely controls P availability (e.g., Demars and Harper, 2002; Rozan et al., 2002). Seasonally, a portion of the P sorbed to Fe(III) oxides in lake sediments is released when FeS and FeS2 form under reducing conditions (Caraco et al., 1993; Gächter, 2003) and then P is available for algal uptake in the water column. In an anoxic lake in northeastern Germany, Kleeberg (2002) found that Fe-bound P in sediments ranged from 12% under anoxic, sulfidic conditions to 28% when oxidized. In that study, 73% of the total P flux between sediments and the water column was recycled in the surface sediments. Especially in eutrophic lakes, high concentrations of P in surface sediments (Kaiserli et al., 2002) coupled with long residence times (Kleeberg, 2002) virtually ensure that algal production is driven to a large extent by internal P loading under mineral, not organic, control (Nürnberg, 1984). Our results are in agreement with these findings in that we found a strong relationship between sediment Fe and P but a weaker, nonsignificant relationship between C and P (Table 1). Although we did not complete any studies to determine underlying causal mechanisms, production of algal biomass in the water column is reliant on P availability, and seasonal storage of P in sediments and release to the water column appear to be more directly under inorganic, mineral control.

In contrast, weight percent biogenic silica and weight percent organic matter are positively correlated in surface sediments (Table 1). Biogenic silica often is used in limnological studies as a proxy for algal production by diatoms (e.g., Colman and Bratton, 2003). In Lake Matoaka, visually the most extensive algal blooms occur in the College Creek arm and in the upper reaches of small coves where BSi and organic matter concentrations are relatively high (Fig. 3). Although Gallinari et al. (2002) have described changes in the dissolution properties of BSi over seasonal time scales, our surface sediment samples all were collected at the same time of year. Thus, we attribute the spatial differences in BSi as a function of the relative amounts of diatom production and deposition throughout the lake. In turn, the elevated concentrations of BSi in deltaic deposits downstream of more-developed subwatersheds indicate that algal production has been preferentially stimulated in these regions (Fig. 5).

Lake-wide, the spatial variation in C to N ratios suggests greater input of allochthonous organic matter in the shallow delta regions of the lake relative to deeper regions (Fig. 4). Aquatic plant debris has a C to N ratio typically between 4 and 10 (Meyers et al., 1995), whereas the high structural C content of terrestrial plants drives the C to N ratio of organic matter much higher (Brenner et al., 1999). In the present study C to N ratios were almost always greater than 20 in more shallow surface sediments adjacent to stream discharge sites, but less than 20 throughout the deeper portions of the lake. Other researchers have suggested that C to N ratios may be insensitive to differences in the relative deposition of allochthonous and autochthonous organic matter if inorganic N concentrations are high (Sampei and Matsumoto, 2001). In Lake Matoaka, C and N are significantly correlated (Table 1), indicating that most sediment N is organic. Thus, the observed pattern of higher C to N ratios in surface sediments near stream discharge sites is consistent with greater deposition of organic matter from upland sources.

The environmental quality of sediments deposited in stream deltas since 1930 shows that biogenic silica is elevated downstream from developed subwatersheds and is much lower downstream from less-developed subwatersheds (Fig. 5). Further, sediment P content on average is nearly twice as high downstream of more-developed subwatersheds (Table 2), suggesting that P availability and algal production are linked. Because P and silica are limiting nutrients for algal growth, algal production (specifically diatoms) should increase as P and BSi input to the lake increase (Cawley et al., 1999). DeMaster et al. (1996) suggest that preservation efficiencies of BSi and P differ in sediments, and in the present study a direct correlation between the concentrations of these nutrients was not found (Table 1). Significantly higher average concentrations of both P and BSi downstream of more-developed subwatersheds (Table 2), however, support the notion that accelerated transition to a hypereutrophic state is being driven by increased algal production due to upland development. Further, because elevated silicate tends to enhance P release from sediments (Koski-Vähälä et al., 2001), the positive feedback of increased internal P loading and diatom production could accelerate lake eutrophication.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
This paper reports on variation in sediment characteristics in a small, man-made lake on the Virginia coastal plain, where terrestrial loadings are most evident in regions of stream discharge. Sediments in these regions are characterized by high C to N ratios and higher BSi and P concentrations downstream of more upland development. These patterns of nutrient enrichment that also have been documented for the entire Chesapeake Bay drainage basin (Colman and Bratton, 2003) highlight the link between terrestrial delivery of materials and aquatic system response (in this case, the transition to a eutrophic state). Lake Matoaka is just one of approximately 4500 impoundments in Virginia and over 2.6 million small impoundments estimated nationwide (Smith et al., 2002). Small impoundments respond rapidly to upland development and thus are good models for regional landscape changes that occur over more extensive spatial and temporal scales.


   ACKNOWLEDGMENTS
 
Thanks to Scott Van Benschoten for field assistance and Timothy Russell and Daniel Thomas for GIS support. This work was supported by the Jeffress Memorial Trust and is Publication 004 of the W.M. Keck Environmental Field Laboratory.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 


Related articles in JEQ:

This Issue in Journal of Environmental Quality

JEQ 2004 33: 413-418. [Full Text]  




This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Related articles in JEQ
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Agricola
Right arrow Articles by Pensa, M. A.
Right arrow Articles by Chambers, R. M.
Related Collections
Right arrow Surface Water Quality
Right arrow Biogeochemical Processes
Right arrow Watershed and Landscape Processes
Right arrow Nutrients
Right arrow Nutrient Cycling

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Vadose Zone Journal Journal of Plant Registrations
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal