Landcover

An understanding of landuse/landcover is integral to water quality planning and evaluations. Because of differences in cultivation practices, crop types are particularly relevant. National Agriculture Statistics Service 2004 crop type data were acquired for Arkansas, Mississippi, and Missouri. The NASS datasets are created annually through a multi-date classification of satellite imagery. Full metadata can be found at http://www.nass.usda.gov/research/Cropland/ metadata/meta.htm. Because the primary purpose of the NASS data is mapping crop types, users should refer to the ancillary Forest Cover and Aquaculture datasets to assess the most accurate extent of the landuse practices. Additionally crop type acreage summaries are included in the attributes of the 8-digit HUC watershed dataset.

Aquaculture

Because of the prominence of catfish aquaculture in the LMAV and the incomplete coverage of this cover type in the NASS data, DU developed a current, as of January 2005, coverage of catfish aquaculture for the entire LMAV. Aquaculture features were digitized based on well defined and visible levees and cross referenced with the 2004 NASS Crop Type Data. Units had to be consistent with NASS data to be included in the aquaculture database. If an area had well defined levees and NASS had that area defined as something other than aquaculture or water it was omitted from the aquaculture database. For the state of Louisiana there were no available NASS data to reference. Therefore, only those aquaculture units that were obviously catfish ponds were included in this database.

Geomorphology: Slope and soils

Besides landcover/croptype, several other site-specific factors influence soil erosion and run-off rates. Particularly notable are slope and soil characteristics as determinant factors in erodability. DU calculated slope for the entire LMAV using the USGS National Elevation Dataset. Prior to calculating slope, all NED panels for the entire LMAV were mosaiced together and all sinks were filled to minimize data anomalies. Slope values are represented in percentages. DU collaborated with the USDA Forest Service to create a Soil Moisture Index (SMI) for the LMAV. Precise in situ measurements of soil moisture are difficult to acquire for large geographic areas such as the LMAV. The conservation partners that have interests in the LMAV realize that information about soil characteristics is vital to determining optimal locations for reforestation and wetland restoration. The SMI was created for use as a surrogate for digital hydric soils data for the LMAV using Landsat satellite imagery acquired during the drought conditions of winter 1999. Using winter drought imagery ensured a more accurate evaluation of soil moisture-retention capacity by minimizing the effects of vegetation in agricultural fields and surface water in satellite imagery analysis. The imagery was classified using an unsupervised classification technique into five soil moisture categories and an open water class. SMI values were only determined for bare soil sites; all sites with ground cover were not assigned a class value. On the ground accuracy assessment affirmed distinct relationships between surface soil moisture, sinks, and existing hydric/non-hydric soil maps. Though these data were developed for evaluating soils capacity to retain water for wetland restoration planning, other characteristics of soils can also be inferred from SMI values. For example, high SMI soils are likely to be of smallest particle sizes and easiest transportability.