Impacts of Reforestation and Deforestation upon Surface Water Quality in Mississippi River Basin

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1 Impacts of Reforestation and Deforestation upon Surface Water Quality in Mississippi River Basin Ying Ouyang, PhD Research Hydrologist Center for Bottomland Hardwoods Research Southern Research Station, USDA Forest Service Starkville, Mississippi, USA Presented at the 2015 Mississippi Water Resources Conference in Jackson, Mississippi April 7-8, 2015 LMRAV

2 Objectives Impacts of deforestation on water quality in MRB, especially in Lower Mississippi River Basin Benefits of reforestation/afforestation upon water quality and flood attenuation Knowledge gaps and recommendations for future research in reforestation for water quality improvement

3 Mississippi River Mississippi River Basin Largest river in USA and third longest river in the world Average discharge into Gulf of Mexico is 380 km 3 /y Problems in MRB Increased nutrient, sediment, and pollutant loads Increased extent and severity of seasonal hypoxic zones Altered aquatic and wetland species compositions Decreased overall health of terrestrial ecosystems GOM

4 Deforestation in MRB Deforestation - Clearing or destruction of forested lands for agricultural productions, building constructions, and timber harvestings In LMRB, about one-half of the original forests were cleared between early 1800s and 1935 A later surge in forest clearing for agriculture took place in the 1960s and 1970s due to a rise in soybean prices Only about 2.8 million ha of bottomland hardwood forests in LMRAV exist today from the original 11 million ha before 1780

5 Consequences of Deforestation on Ecology, Hydrology, and Climate Change Ecological consequence Loss of habitat and biodiversity through the destructions of biological community structure and extinction of species Hydrological impacts Flooding Loss of infiltration capacity, litter water absorption, and canopy water interception Result in acceleration of surface runoff at the expenses of reducing groundwater recharge and increasing flood frequency

6 Hydrological impact (continued) Increased surface runoff may enhance pollutant, nutrient, and sediment loads into streams Climate consequence Carbon sequestration and CO 2 fixation reduction resulted from the loss of trees LMR GOM

7 Impacts of Deforestation on Water Quality N pollution in streams Mean N load from MRB into GOM is about 1.2 million MT/y A 500% increase in N fertilizer application from to is the primary contributor to a 200% increase in nitrate-n export from MRB to GOM Of which, corn and soybean cultivation accounts for 52% and atmospheric deposition accounts for 16% Concentrations of nitrate-n in stormwater are 50% to 100% greater than in the baseflow water in MRB

8 Impacts of Deforestation on Water Quality P pollution in streams Mean TP load from MRB into GOM is 0.15 million MT/y Of which, pasture and rangelands account for 37%, corn and soybean cultivation accounts for 25%, other crops account for 18%, and urban sources account for 12% TP content in the sediment is about 2.5 times greater than in the surface water in MRB Inorganic P is an order of magnitude higher in the stormwater than in the baseflow water in MRB

9 Impacts of Deforestation on Water Quality About 70% of N and P exported to GOM is from agricultural practices Seasonal variations of TN, TP, and turbidity: spring > winter > summer > fall due to the agricultural practices and wetland drainages

10 Impacts of Deforestation on Water Quality Annual nitrate-n load (millions of metric tons) y = x R² = Area of hypoxic zone (thousands of km 2 ) An increase in 1,000,000 MT of nitrate-n flux into the GOM would increase the hypoxic zone by 67.8 km 2 annually

11 Impacts of Deforestation on Water Quality Sediment in streams Overall, the MR carries roughly 550 million MT of sediment into the GOM each year Turbidity in the Mississippi Delta streams range from 8 to 2328 NTU Very few research efforts have been directly devoted to linking deforestation to sediment erosion in the MRB

12 Reforestation Afforestation is the establishment of a forest or stand in an area where the preceding vegetation or land use was not a forest Reforestation is the reestablishment of forest cover, either naturally or artificially, that usually maintains the same forest type and is done promptly after the previous stand or forest was removed

13 Reforestation Over the 10-year period from 1980s to 1990s, about 77,698 ha have been reforested in the LMRB and oaks are the most commonly planted species Planting seedlings method is preferred over direct seeding method for a quick reforestation A successful reforestation requires an understanding of site soil and hydrological conditions and matching species preferences and tolerances to the site conditions

14 Benefits of Reforestation on Water Quality Forests produce clean water for drinking water supply, provide fish and wildlife habitat, recover ecosystem service, and furnish human recreation Trees absorb rainfall, slow down flow velocity, disperse surface runoff, offset water discharge, filter pollutants, and reduce excess nutrient and sediment load into the rivers and streams Reforestation is an important measure for improving vegetation coverage, water quality, flood control, and water resources sustainability A reduction of 40% N load into the GOM is possible through reforestation, restoration of wetlands, and establishment of riparian buffers

15 Vegetated filter strip (VFS) One of the reforestation methods for reducing loads of sediments and their associated pollutants such as hydrocarbons, metals, and nutrients into streams A 20-m wide of VFS is effective to reduce runoff nutrient concentrations below their target levels Forest BMPs Reforestation Methods Forest BMPs can reduce 60-80% TN and 85-86% TP loads, and 53-94% sediment erosion

16 Impacts of reforestation methods upon N, P, and sediment reduction from different locations in the MRB Location Method Nitrogen Reduction Phosphorus Reduction Sediment Reduction Reference Illonoise River-fed constructed wetlands 171 g N m 2/ y Phipps and Crumpton, 1994 Ohio River-fed constructed wetlands g N m 2 /y Spieles and Mitsch, 2000 Caernarvon, Luisana Mississippi River wetland restoration 10 g N m 2 /y Lane et al., 1999 Chesapeake Bay Riparian forest buffer g N m 2 /y Peterjohn and Correll, 1984 Chesapeake Bay Restored riparian wetland 6.9 g N m 2 /y Lowrance et al., 1985 Chesapeake Bay Young hardwood riparian forest 4.3 g N m 2 /y Lowrance et al., 1985 MRB and GOM Restoration of wetlands and riparian ecosystems 40% Mitsch et al., 2001 Pearl River, Mississippi Rivercane buffer 0.23 cm/mon Jolley et al., 2009 Southern Illinois Riparian buffer with rivercane 99% from groundwater NO - 3 Schoonover and Williard, 2003 Southern Illinois Riparian buffer with rivercane 100% reduction from runoff water 100% from runoff water Schoonover et al., 2006 LMAV Forest BMP % nutrients Kroger et al., 2013 North Carolina Reforestation from agriculture land 0.06 T/acre/y Douglass and Swank, 1975 James Creek Watershed, Mississippi Forest land T/acre/d Simon et al., 2002 North Mississippi Reforested watersheds 88 g/ha (mean TP in solution) Duffy, 1978 North Mississippi Reforested watersheds 210 g/ha (mean TP in sediment) Duffy, 1978 Nutrient and sediment reductions vary with reforestation methods and locations

17 Simulating impacts of Reforestation on Water Quality Using BASINS-HSPF Model Fig. 1. Location of Yazoo River Basin Fig. 2. Land use cover for LYRW

18 Simulation Scenarios Scenario 1 Predict water outflow, sediment and nutrient load in the LYRW without converting agricultural land into forests Scenario 2 Predict water outflow, sediment and nutrient load in the LYRW with converting 25, 50, 75, and 100% of agricultural lands near the bank into forests Comparison of two scenarios to evaluate the potential impacts of reforestation upon water quality and river discharge

19 Impacts of Reforestation on Water Outflow Attenuation, and Nutrients/Sediment Load Reduction A conversion of agricultural land into forests attenuated water outflow as well as reduced sediment/nutrient loads Over a 10-year simulation, the water outflow attenuation was 250m 3 /ha/y Over a 10-year simulation, the sediment, nitrate-n, and phosphate load reductions were, respectively, 4.02, 0.06, metric ton/ha/y Reforestation in or around the bank of streams is a useful practice for water outflow attenuation, and sediment and nutrient load reduction Because forests absorb water and reduce the surface water runoff, and thereby decreasing peak flows and reducing sediment/nutrient load into the streams

20 Research Needs in MRB Very few field experimental data are available for investigating the benefits of reforestation Paired watershed experiments (i.e., with and without reforestation) are necessary to elucidate the impacts of reforestation on water quality and flood control Since these impacts are highly dynamics, it is difficult and expense to quantify them by field experimentation alone Research should be directed toward the application of watershed models in conjunction with field measurements

21 Research Needs More studies are needed to estimate the forestry BMPs efficacies regarding the reduction of nutrient export into GOM While vegetative filter strip (VFS) is one of the best reforestation methods, the most effective way to establish the VFS strip deserves a further investigation While N is traditionally considered as the most important nutrient for phytoplankton growth, P could be a factor for phytoplankton production

22 Research Needs Insufficient attentions have been paid to evaluate the benefits of reforestation on restoration of wildlife habitat, biodiversity, and soil stability and further study is needed in this regard Forests can mitigate the accumulation of CO 2 in the atmosphere by absorbing this gas from the air for photosynthesis. Half of the carbon absorbed is released back to the atmosphere during respiration, while the other half is sequestered in soils, sediments, and wood Research should be initiated to investigate the impact of reforestation on carbon sequestration

23 Summary Impacts of deforestation on water quality and flooding Benefits and methods of reforestation and afforestation on water quality improvement and flood attenuation Knowledge gaps of reforestation Recommendations for further study