Land Use Changes and Increased Nitrogen Export

th
10
Quantifying land use effects on the provisioning of ecosystem services to
inform local planning
Laura M Early and Laurie A Fowler – River Basin Center, Odum School of Ecology, UGA
Introduction
Georgia’s coastal plain is largely rural with clusters of urban and suburban development along the coast and highways. The coastal plain region is rich in ecosystem and species diversity, and the region relies economically on many of the services these ecosystems provide such as water purification, hydrologic stability, and outdoor recreation opportunities. Two of the greatest identified threats to coastal Georgia ecosystems are unplanned and unrestricted growth and development, and reluctance to embrace conservation planning (Dobbs Foundation 2011). With an exponentially growing population, it is imperative to understand how human activities like land use change are effecting biodiversity, ecosystem functions, and the services they provide (MEA 2005).
Excess nutrients (nitrogen and phosphorus) are one of the leading causes of water pollution and loss of biodiversity in aquatic systems worldwide (Cardinale 2011). Nutrient loading is influenced by land use and land cover types, and in this study, we use Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) to model the provisioning of water purification services at alternate land use scenarios. Because nitrogen is one of the most abundant water pollutants worldwide, we use its modeled movement across the landscape as a proxy for water pollution in this watershed.
Local land-­‐‑use planning exercises and policies facilitate economic growth and development, as well as conservation of vulnerable ecosystems. Georgia state law requires local governments with zoning or land development regulations to include a land use element in their comprehensive plans, and it is recommended that all local governments partake in land-­‐‑use planning (OCGA 110-­‐‑12-­‐‑1). Four counties in the Satilla watershed (Camden, Coffee, Glynn, and Ware) included Future Land Use Maps in their Joint Comprehensive Plans, and these were incorporated into the inputs of the water purification InVEST model.
InVEST is an open-­‐‑source spatially explicit software that models a suite of 16 ecosystem services to aid researchers and decision-­‐‑makers in examining tradeoffs in the provisioning of services between different land-­‐‑use options (Sharp et al. 2015). For this study, we used the water purification model to assess how the local governments’ plans will affect nutrient loading in the Satilla River Watershed.
Methods
Discussion
InVEST Water Purification model uses GIS datasets (precipitation, soil types and depths, vegetation types) to calculate annual average runoff from each cell across a landscape, and then uses nutrient retention and export coefficients for each land cover type to determine the amount of nitrogen and phosphorus that is retained and exported at the sub-­‐‑watershed level on an annual basis. We used two land use scenarios to assess the change in water purification services at the land use pa_er envisioned by local planners.
Overall, both nitrogen and phosphorus export was greater under the Comprehensive Plan Scenario than under the Current Land Use Scenario. Nitrogen loading more than tripled in the watershed, and phosphorus loading increased six-­‐‑fold.
Scenarios
b)
Future Scenario:
Comprehensive Plan
Current Land Use
Adapted Future Land Use Maps from local Comprehensive Plans of Camden, Coffee, Glynn, and Ware Counties into a land cover dataset, keeping the rest of the watershed at the current land use.
Combined GAP 2001 and NLCD 2011 land cover datasets to capture multiple ecosystems and more recent developed land uses.
FIGURE 4: Future Scenario Use/Land Cover map, and !
percentage of watershed in specified land use/land covers.
FIGURE 3: Current Land Use/Land Cover map, and percentage of watershed in specified land use/land covers.
Forests
Managed Pine Plantations
Developed, Open Space
Developed, Low
Other
Cultivated Crops
Forested Wetlands
Developed, Med
Developed, High
Results: Change in Nutrient Exports
a)
b)
Change in Total Nitrogen
Export
Change in Total Phosphorus
Export
650,190
P
25,155
169,468
144,313
Spatial extent of land use change across the watershed is also important, as seen in the change in nutrient export per sub-­‐‑watershed. N and P show similar pa_erns of change: increasing in sub-­‐‑
watersheds where land use changed, staying the same in sub-­‐‑watersheds where no land use change occurred, and only decreasing at the coast. This decrease could be due to the expanse of marshes along Georgia’s coast and their ability to uptake excess nutrients. To further understand which land use changes have the most impact on increasing nutrient export, we examined land use changes between scenarios in the top 5 nitrogen exporting sub-­‐‑
watersheds. The most common change in sub-­‐‑watershed 82 from forestry to cultivated crops suggests that forestry parcels retain more and/or export less nutrients to streams. This could be an important note, as forestry is one of the major land uses in the Satilla Watershed, and 3 of the 4 Comprehensive Plans used in this study allowed for a significant expansion in agriculture. The majority of sub-­‐‑watershed 73 stayed as natural land cover, while the model predicted it to have one of the highest increases in nitrogen export. However, 73 is downstream of 108, in which the most common land use change was from natural to medium density development, demonstrating that downstream effects of development may overpower natural ecosystems’ ability to remediate. This analysis may be particularly useful in the planned revision of comprehensive plans with land use elements in Coffee County, Ware County, and Camden County over the next five years.
FIGURE 5: Difference (Comprehensive Plan Scenario-­‐‑-­‐‑Current Scenario) in total nitrogen (a) and phosphorus (b) export per sub-­‐‑watershed in kg/
year. There was no difference in export for sub-­‐‑watersheds that experienced no land use change between scenarios. Reds indicate the highest increase in nutrient export, and greens indicate no change or decrease in nutrient export for the sub-­‐‑watershed.
Future Research Directions
Land Use Changes and Increased Nitrogen Export
•  Incorporate TMDLs into models
•  Additional scenario to represent a lower-­‐‑
impact development pa_ern, buffers on streams, preserve forestry parcels
Land Use Change to Medium Density Development
Most Common Land Use Change
40
NaturalàForestry
WS 73
NaturalàDev. Med
NaturalàNatural
ForestryàCropland
Percent of Subwatershed
WS 15
WS 82
WS 108 NaturalàDev. Med
•  Model provisioning of additional ecosystem services: coastal fisheries, recreational opportunities, carbon sequestration
25
20
15
10
Acknowledgements
0
natural->dev. Med
forestry->dev. med
harvested->dev. med
WS 12
Table 1: Most common land use change in each of the top 5 sub-­‐‑
watersheds with increased nitrogen export.
Increase in Intensity of Development
16
14
12
10
8
6
4
2
0
30
5
Cardinale, BJ. (2011) Biodiversity improves water quality through niche partitioning. Nature: 472. pp. 86–91.
Dobbs Foundation. (2011) “Environmental State of the State: Georgia Coast.”h_p://www.dobbsfoundation.org/Dobbs_Foundation_Georgia_Coast_2011.pdf
Millennium Ecosystem Assessment: Living Beyond our Means—Natural Assets and Human Well-­‐‑being. (2005) World Resources Institute, Washington, DC.
OCGA 110-­‐‑12-­‐‑1. Minimum Standards and Procedures for Local Comprehensive Planning. Sharp, R. et al. (2015) InVEST +VERSION+ User’s Guide. The Natural Capital Project, Stanford University, University of Minnesota, The Nature Conservancy, and World Wildlife Fund.
916,172
Through a spatially-­‐‑explicit ecosystem services analysis of the current land use/land cover and future development plans developed by local governments, we can be_er understand the threats development pa_erns pose to ecological systems. Careful planning of future development may lessen impacts to vulnerable coastal ecosystems and the services they provide to the growing population.
35
Literature Cited
265,982
TABLE 2: Total Nitrogen and Phosphorus Exports for the Satilla River Watershed in kg/yr. Conclusions
WS 12
FIGURE 2 : There are 21 impaired stream segments based on dissolved oxygen levels in the Satilla River watershed. Total Maximum Daily Loads (TMDLs) for nitrogen and phosphorus have been established for each of these segments. (Image: GA EPD)
N
Common nonpoint sources of nitrogen and phosphorus pollution include agricultural fertilizers, wastewater treatment outflows, and septic systems. With this shift in land use over the watershed, the increase in nutrient loading is expected.
FIGURE 1: a) Georgia Watersheds (Image: GA DNR). b) Counties encompassed by Satilla Watershed.
The Satilla River watershed is entirely within the coastal plain, encompassing ecologically important areas including protected barrier islands, saltmarshes, marsh hammocks, forested wetlands and upland forests. The watershed is largely rural, but includes urban centers in Camden, Coffee, Glynn, and Ware Counties. Comp. Plan Change in Export
In the Comprehensive Plan Scenario the percentage of the watershed in agriculture increased from 10.5% to 24.2%, as did the percentage of land in medium density development from 0.47% to 9.03%. Simultaneously, the percentage of the watershed in natural forests, forested wetlands, and managed forestry decreased from the Current Land Use Scenario to the Comprehensive Plan Scenario. Study Area: Satilla River Watershed
a)
Current
Percent of Subwatershed
!
Annual Georgia Environmental Conference
early succession->dev. med
WS 15
WS 73
WS 82
late successioin->dev. Med
dev. open space->dev. med
dev. low->dev. med
WS 108
FIGURE 6: The 5 sub-­‐‑watersheds in the study area for increased nitrogen area were selected. For each, the land cover types that would be converted into medium density development under the Comprehensive Plan Scenario are shown as a percentage of the sub-­‐‑watersheds’ land area.
Special thanks for guidance, insight, and resources from the Fowler Lab, Odum School of Ecology, Southern Georgia Regional Commission, Coastal Georgia Regional Commission, Bob Islar, Satilla Riverkeeper, One Hundred Miles.
dev. open
dev. open
space->dev. low space->dev.
med
WS 12
dev. open
space->dev.
high
WS 15
dev. low->dev. dev. low->dev. dev. med->dev.
med
high
high
WS 73
WS 82
WS 108
FIGURE 7: In all of the highest nitrogen-­‐‑exporting sub-­‐‑
watersheds, increasing the intensity of development in areas that are already developed accounted for a very small portion of land use change. Future modeling should explore the tradeoffs of increasing density of development in lieu of developing natural areas.
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