Nutrient.docx

1、NutrientNUTRIENT TRANSPORT DURING BIOREMEDIATION OF CRUDEOIL CONTAMINATED BEACHESBrian A. Wrens (Environmental Technologies & Solutions, Rochester, NY)Michel C. Boufadel and Makram T. Suidan (Univ. of Cincinnati, Cincinnati, OH)Albert D. Venosa (U.S. EPA, Cincinnati, OH)ABSTRACT: The effect of wave

2、energy on transport of dissolved nutrients in the intertidal zone of sandy beaches was studied by comparing the washout rates of a conservative tracer (lithium) on two beaches in Maine. The physical characteristics of the two beaches were similar, and they were subjected to the same tidal influences

3、, but the wave energies were very different. Scarborough Beach is a high energy beach that faces southeast toward the Atlantic Ocean, whereas Ferry Beach is in a protected harbor. This difference in wave energy caused lithium to be washed out of Scarborough Beach much more rapidly than from Ferry Be

4、ach. The higher wave energy at Scarborough Beach also appears to have increased the amount of lithium that was diluted directly into the water column. These differences in transport rate and mechanism have important implications for the feasibility of bioremediation for cleanup of oilcontaminated sh

5、orelines.INTRODUCTIONThe growth rate of oildegrading bacteria on contaminated shorelines is often limited by the availability of nutrients, such as nitrogen and phosphorus (Pritchard and Costa, 1991; Bragg et al., 1993; Lee et al., 1993; Venosa et al., 1996). Effective bioremediation requires nutrie

6、nts to remain in contact with the oiled beach material, and the concentrations should be sufficient to support the maximal growth rate of the oildegrading bacteria throughout the cleanup operation. Contamination of coastal areas by oil from offshore spills usually occurs in the intertidal zone, wher

7、e the washout of dissolved nutrients can be extremely rapid. Lipophilic and slowrelease formulations have been developed to maintain nutrients in contact with the oil (Atlas and Bartha, 1992), but most of these rely on dissolution of the nutrients into the aqueous phase before they can be used by hy

8、drocarbon degraders (Safferman, 1991). Therefore, design of effective oil bioremediation strategies and nutrient delivery systems requires an understanding of the transport of dissolved nutrients in the intertidal zone.Transport through the porous matrix of a beach is driven by a combination of thre

9、e main factors: tide, waves, and the flow of freshwater from coastal aquifers. The focus of this research was on the effects of tide and wave activity. Tidal influences cause the groundwater elevation in the beach, as well as the resulting hydraulic gradients, to fluctuate rapidly (Nielsen, 1990; Wr

10、enn et al., 1997). Wave activity affects groundwater flow through two main mechanisms. First, when waves run up the beach face ahead of the tide, some of the water percolates vertically through the sand above the water line and flows horizontally when it reaches the water table (Riedl and Machan, 19

11、72). Waves can also affect groundwater movement in the submerged areas of beaches by a pumping mechanism that is driven by differences in head between wave crests and troughs (Riedletal. 1972).The relative effects of tide and waves on nutrient transport in the intertidal zone of sandy beaches was in

12、vestigated by comparing the washout of a conservative tracer, lithium, on two beaches in southern Maine. Scarborough Beach is a high energy beach that faces the Atlantic Ocean, whereas Ferry Beach is in a sheltered harbor at the mouth of the Scarborough Marsh. Lithium transport atFerry Beach was dri

13、ven almost exclusively by tidal effects, whereas tide and waves both affected transport at Scarborough Beach.EXPERIMENTAL DESIGNSite Description. The two beaches used in this study are subjected to very different wave energies, but in other respects they are quite similar. Both are composed primaril

14、y of medium to fine sand with relatively narrow particle size distributions. Differences in the composition of the two beaches suggest that the hydraulic conductivity of Scarborough Beach might be slightly larger than Ferry Beach, but the small permeability differences were expected to have much les

15、s influence on solute transport than the differences in wave energy. The tide was identical at both sites.Plot Setup and Sample Collection. The tracer was applied to the beach in discrete areas called plots. Each plot was 5 m wide (i.e., parallel to the shoreline), and they were either 10 m (Ferry B

16、each) or 12 m (Scarborough Beach) long (i.e., perpendicular to the shoreline). Although the plots on Ferry Beach were shorter than those on Scarborough Beach, the difference in elevation between the tops (i.e., the landward edges) and the bottoms (i.e., the seaward edges) of the plots was approximat

17、ely the same on both beaches. The plots were set up such that the landward edges were at the elevation that was expected for the highest tide that would occur during the study.A transect consisting of six multiport sample wells was installed perpendicular to the shoreline through the center of each

18、plot. The layout of these transects and the elevations of the tops and bottoms of the plots on both beaches are shown in Figure 1. Three of the six sample wells were installed inside the plots, one well was installed landward of the plots, and two were installed seaward of the plots. Figure 1 also s

19、hows the locations of the sample ports for each well.Sprinklers were used to apply the tracer to the beach surface inside the plot boundaries at low tide. Lithium nitrate (99.7%; Cyprus Foote Mineral Co., Kings Mountain, NC) was dissolved in 100 gallons of fresh water to a final concentration of 33

20、g/L, which gave it a density approximately equal to the local seawater. Water samples were collected from the multiport wells periodically for about two weeks.Water Level Measurement. The water levels in the beaches were measured with transects of six piezometer wells that were installed perpendicul

21、ar to the shoreline. Piezometer wells were installed at the top, bottom, and middle of the plots. One well was landward of the top, and two were seaward of the bottom of the plots. The most seaward well, which was screened over a fourfoot interval above the beach surface, was used primarily to measu

22、re the level of the tide whenever it was high enough to submerge any part of the sample well transects. Vibrating wire piezometers (RocTest, Inc., Plattsburgh, NY) were used to measure the water level at each well position. Three readings were usually taken for each piezometer every 15 minutes. Thes

23、e three readings were averaged to smooth out the effect of waves on the water level measurements.RESULTS AND DISCUSSIONHydraulic Gradients. The two main forces that drive solute transport in sandy beaches are waves and tidally induced hydraulic gradients. Although no quantitative measurements of the

24、 wave activity at the two beaches used in these studies are available at this time, a qualitative comparison can be made by inspection of Figure 1. Whereas the water level changed fairly smoothly at Ferry Beach in1.0oy 3 sL)no o.4)o._4,234:10time (days) 0.5 0.0 0.5 , . . . . . beach surface Ferry Be

25、ach tide l l (low energy) tpOIPOtf1.0bottom of plots I +sampling wellsbeach surfacerScarborough Beach(high energy). .( ) I, ,_ , , _10top Of plotstide _,I .rbottom of plots. o20distance from top of plots (m)30FIGURE 1: Beach profiles showing well positions and the elevations of the tops and bottoms

26、of the experimental plots (i.e., the areas to which the tracer was applied). The circles on each well mark the depths of the sample ports. All elevations were measured relative to a benchmark, but the absolute elevations of the benchmarks on the two beaches were not the same. The tide measurements s

27、how that the absolute elevations of the plots were similar on both beaches. Time is measured relative to the beginningof the experiment (i.e., when the tracer was applied).0.040.02 0.004,._ 0.02._ 0.04 c5s 0.060.08response to the tide, the response was quite jagged at Scarborough Beach. Although mul

28、tiple readings were taken whenever water level measurements were made, it was not possible to completely eliminate variations due to waves from the Scarborough Beach data.The effects of waves can also be seen in Figure 2, which shows the hydraulic gradients in the bottom (seaward) half of the plots

29、for both beaches. The response at Ferry Beach was relatively smooth, whereas the gradient fluctuated rapidly at Scarborough Beach. Wave run up and subtidal pumping probably both contributed to these abrupt changes in the hydraulic gradient. In general, the responses of the hydraulic gradients to the

30、 tide were similar in both beaches. For example, landwarddirected (i.e., positive) hydraulic gradients developed only briefly in this region of both beaches. (Landwarddirected gradients persisted much longer in the top half of the plots, however.) Most of the time, the hydraulic gradients were direc

31、ted seaward (i.e., negative), which is consistent with previous observations (Nielsen, 1990; Wrenn et al., 1997).time, Ferry Beach (days) 1.0 0.5 0.0 0.5 1.0Scarborough BeachI. Il1 .0Ferry Beach . . . . . . . . . . . . . .0.00.5time, Scarborough Beach (days)1.0FIGURE 2: Hydraulic gradients in the bo

32、ttom half of the plots at Ferry and Scarborough Beaches. Positive values indicate landwarddirected gradients and negative values indicate gradients that are directed seaward. The time is measured relative to the beginning of the experiment, and the time scales for the two beaches are offset by6 hours to improve readability.Tracer Washout. Lithium was removed from Scarborough Beach much more rapidly than from Ferry Beach. At Scarborough Beach, less th