View Full Table | Close Full ViewTable 1.

Hydraulic characteristics of each oxbow wetland relative to the Minebank Run stream reach from April through July 2008, indicating the extent of connectivity with the adjacent stream reach.

 
Oxbow 1 Oxbow 2
Threshold elevation (Te) 1.55 m 0.67 m
Distance from gauge 91 m (downstream) 30 m (upstream)
Discharge required for exchange† ∼2.8 m3 s−1 ∼0.12 m3 s−1
Recurrence interval for exchange‡ twice a year >8 times a year
Exceedance probability for exchange§ ∼0.26 (%) ∼9 (%)
Rating curve to determine stage–discharge relationship taken from USGS stream gauge # 0158397967, Minebank Run near Glen Arms, MD, water year (WY) 2008.
Estimated recurrence interval (yr) calculated from available peak discharge values for WY 2002–2008 (n = 8).
§ Estimated exceedance probability calculated from 5-min instantaneous discharge values for WY 2008.



View Full Table | Close Full ViewTable 2.

Selected physiochemical characteristics of groundwater (GW) and surface water (SW) in the overlying water column collected from Minebank Run, Stony Run, and Baisman Run study wetlands in September 2008. Grab samples were collected from 3 to 5 minipiezometers and surface water samples from 3 to 5 sampling locations within each wetland. The first column under each site name represents GW samples and the second column represents SW samples.

 
Parameter† Minebank Run Stony Run Baisman Run
Oxbow 1 Oxbow 2 CW1 CW2 CW3 FW1 FW2
GW SW GW SW GW SW GW SW GW SW GWSW GW SW
NH4 + (mg N L−1) 0.06 0.12 0.39 0.38 0.73 —§ 0.58 0.24 0.39 0.3 0.1 0.05
NO3 (mg N L−1) 1.3 0.4 1.0 0.1 0.05 7.95 11.0 0.15 0.16 0.14 0.05
TN (mg N L−1) 1.4 0.5 1.3 0.7 23.0 0.73 0.70 0.56 0.18
TP (μg P L−1) 13.0 4.0 10.0 44.0 8.8 19.2 120 8.42 7.8 62.7 166.7
DOC (mg L−1) 0.62 0.75 1.2 1.6 3.7 4.0 2.5 1.0 10.0 1.1 5.7 0.0 0.73 0.60
DO (mg L−1) 0.92 8.0 1.8 1.8 0.71 0.72 4.85 0.60 1.78 1.79 1.68
Temp. (°C) 18.6 19.6 20.83 19.3 22.1 21.0 21.6 21.5 21.2 20.7 19.4
Cond. (μh cm−1) 980 960 1100 1100 600 750 700 1150 650 70 70
Depth (cm) 0‡ 16 0‡ 25.7 0‡ 0‡ 11.5 0‡ 3.25 0‡ 0‡
NH4 +, ammonium; NO3 , nitrate; TN, total nitrogen; TP, total phosphorus; DOC, dissolved organic carbon; DO, dissolved oxygen; Temp, temperature; Cond., conductivity; Depth; surface water level of the overlying water column in the wetlands the month of September 2008.
Zero indicates no measurement of GW depth.
§ — indicates feature was dry during the sampling period.



View Full Table | Close Full ViewTable 3.

Denitrification rates in the Minebank Run oxbow wetlands relative to the standing stock of NO3 in the overlying water column (OWC) of the wetland and the load of NO3 N carried by the Minebank Run stream.

 
Site Wetland Minebank Run Stream
Wetland area Denitrification rate† Soil NO3 denitrified in the wetland NO3 standing stock OWC‡ NO3 removal % removal Load NO3 % removal by wetlands
m2 μg N kg−1 (sediment) d−1 mg N m−2 d−1 mg N d mg N d−1 mg d−1 mg N d−1
Oxbow 1 412 31.4 24.3 42,840 4.3 23.4 119,970 8.3
Oxbow 2 296 56.2 43.4 44,400 3.5 28.3 119,970 11
Average denitrification rates pooled for summer and winter (n = 10).
Nitrate-standing stock obtained from NO3 concentrations in oxbow 1 and oxbow 2 OWC during time of the experiment, ∼0.2 mg L−1 and 0.3 mg L−1, respectively.
§ Stream NO3 load calculated by multiplying the average annual discharge (129,000 L d−1) for water year 2008 from the USGS Minebank Run stream gauge 015839795 by the average stream NO3 concentration (0.93 mg L−1); data from Paul Mayer USEPA collected April, July, and October 2008.