Nutrient and Sediment Cycling and Retention in Urban Floodplain Wetlands Greg Noe, Cliff Hupp, Nancy Rybicki, Ed Schenk, and Jackie Batson National Research Program, Reston VA U.S. Department of the Interior U.S. Geological Survey Funded by USGS Chesapeake Priority Ecosystem Science
Floodplain nutrient and sediment retention Floodplains are last location in watersheds for significant material retention before river loading into coastal waters What are nutrient cycling and sediment deposition rates? What are the controls? What is the percent retention of river loads by floodplains?
Coastal Plain floodplains trap large nutrient loads 1) Measured sedimentation fluxes in plots 2) Scaled to entire CP extent of floodplain 3) Compared to river load g m -2 yr -1 m 2 g yr -1 Percent retention for 7 rivers: Median Range Nitrogen 22% (5 to 15%) Phosphorus 59% (14 to 587%) Sediment 119% (53 to 69%) Noe and Hupp. 29. Ecosystems.
Hydrogeomorphic controls in floodplain ecosystems Four dimensions of river corridors influence floodplain ecosystem processes through river-floodplain hydrologic connectivity This heterogeneity is critical to the prediction and scaling of floodplain effects on water quality Noe. 213. Treatise of Geomorphology. Modified from NRC 22.
Difficult Run Floodplain Study measuring sediment and nutrient retention along lateral and longitudinal floodplain gradients in an urban, Piedmont watershed Noe. 213. Treatise of Geomorphology.
Number of floods (discharge > 1 cfs) Urbanization influence on flooding 16 14 12 1 8 6 4 2 193 194 195 196 197 198 199 2 21 22 Hupp et al. in review
Difficult Run Floodplain Study measuring sediment and nutrient retention along lateral and longitudinal floodplain gradients in an urban, Piedmont watershed lateral gradients longitudinal gradients
Ecosystem process measurements Mineralization CO 2 flux Hydroperiod Litterfall Sedimentation Bank erosion
Annual net mineralization rates P mineralization (mmol-p m -2 yr -1 ) 8 6 4 2-2 -4 Levee Backswamp Toe slope 1 2 3 4 5 Site 1 2 3 4 5 Site 6 5 4 3 2 1 N mineralization (mmol-n m -2 yr -1 ) downstream downstream Noe et al. in review
Turnover of soil N and P pools Rate Areal mineralization (mmol m -2 yr -1 ) Turnover rate (mol mol -1 yr -1 ) Turnover time (yr) P mineralization 3.6.27 369 N mineralization 319.46 22 % nitrification 66% Noe et al. in review
Sedimentation stimulates mineralization N mineralization ( mol-n m -2 d -1 ) 25 2 15 1 5-5 1:1-1 -15 R 2 =.12 P =.1-2 1 1 1 1 2 1 3 1 4 1 5 1:1 R 2 =.269 P <.1-1 1-1 1 1 1 1 2 1 3 1 4 4 3 2 1 P mineralization ( mol-p m -2 d -1 ) N sedimentation during incubation Estimated P sedimentation during incubation ( mol-n m -2 d -1 ) ( mol-p m -2 d -1 ) Noe et al. in review
Plant uptake vs. mineralization Vegetation N uptake litterfall and herbaceous ( mol-n m -2 d -1 ) 25 2 15 1 5 5 1 15 2 25 N mineralization ( mol-n m -2 d -1 ) 1:1 r =.371 P =.52 2 r =.57 P =.775 2 4 6 8 1 P mineralization ( mol-p m -2 d -1 ) 1:1 1 8 6 4 Vegetation P uptake litterfall and herbaceous ( mol-p m -2 d -1 ) Rybicki et al. in prep.
N sedimentation (g m -2 yr -1 ) 25 2 15 1 5 Levee Backswamp Toe slope Nutrient sedimentation rates downstream 5 4 3 2 1 P sedimentation (g m -2 yr -1 ) N Sedimentation (g m -2 yr -1 ) 3 25 2 15 1 5 1 2 3 4 5 Site Pocomoke Mill Stream Tangipahoa VA Piedmont Difficult Mattaponi Chickahominy Roanoke 1 2 3 4 5 Site Pocomoke Mill Stream Tangipahoa Roanoke Difficult Mattaponi Chickahominy 1 8 6 4 2 P Sedimentation (g m -2 yr -1 )
Geomorphic controls on sediment retention and loss Sediment gain or loss (kg m -1 yr -1 ) Floodplain Trapping Factor 15 1 5-5 6 5 4 3 2 1-1 Floodplain Banks Net Site Site 1 Site 2 Site 3 Site 4 Site 5 Net trapping factor Gross trapping factor -2 Site Site 1 Site 2 Site 3 Site 4 Site 5 Hupp et al. in review
Historic mill dams and legacy sediment 2.5 m 41% of mainstem length impounded Plank road Dam locations from FCPA Hupp et al. in review
Urban, Piedmont floodplain is retentive g m -2 yr -1 (average all floodplain plots) N net flux = + 11.43 P net flux = + 2.35 Sediment net flux = + 3984 14.9 2.89 576 7.8.65 2.66.54 192 4.47.11 Noe. 213. Treatise of Geomorphology.
Correlations among ecosystem processes Hydroperiod DIN load N sed. P sed. SRP load CO 2 flux N mineralization P mineralization N plant uptake P plant uptake
Nutrient and Sediment Cycling and Retention in Urban Floodplain Wetlands Urban floodplain wetlands can still remove pollutants Despite legacy sediment, mill dams, and stormwater High nutrient and sediment inputs Efficient internal cycling of nutrients Coupled N and P biogeochemical processes High trapping rates relative to watershed losses
ABSTRACT DEADLINE: 12 July 212 (23:59 ET) Tidal freshwater rivers link watersheds with estuaries and affect the flux of carbon, nutrients, sediment, and freshwater from land to the ocean. However, climate change is continually altering tidal river ecosystems as tides advance inland and watershed inputs change. This Chapman Conference will generate synthesis of feedbacks between geomorphic, biogeochemical, and ecological processes in tidal rivers to better predict ecosystem changes in response to climate change. U.S. Department of the Interior U.S. Geological Survey www.agu.org/tidalrivers