Lab 4: To what extent do cattle and agriculture affect water bodies in Wisconsin?

Goal

The goal of this lab was to answer the question: To what extent do cattle and agriculture affect water bodies in Wisconsin?

Background

With a substantial amount of phosphorus runoff from cattle farms and conventional agriculture, Wisconsin lakes and streams can bear a heavy load of this nutrient. Usually a limiting nutrient in water, large inputs of phosphorus put precious bodies of water at risk of an overgrowth of algae and weeds, anaerobic conditions, and even anoxia. A GIS risk assessment of such eutrophication in terms of cattle inventory and fertilized acres per county could make this relationship clear to those who may be unfamiliar with it.

Procedure

First, counties were clipped to the state of Wisconsin using the ESRI2013 database provided by UWEC. Next, data was gathered from the USDA QuickStats online index. This included the amount of fertilized acres and the total amount of cattle inventory by county in Wisconsin. Data were entered into a spreadsheet and imported into ArcMap as a data table

This table was joined to the county attribute table, using “NAME” of the counties layer and “County” of the spreadsheet data. Graduated color maps were then made of both cattle inventory and fertilizer acres, which was normalized by total square miles of each county.  

The two highest levels, based on the Jenks natural breaks classification method, of cattle inventory (>31000 total) and fertilizer use (>161 acres per mile²) were selected and new layers were created for each criteria. In addition, a layer of counties that were both high in cattle inventory and fertilizer use was created using an intersect between them. All layers were put onto a third data frame.

The DNR database offered map data of both impaired lakes and impaired streams. Streams and lakes whose impairment was high phosphorus levels were selected and new layers were created from those selections. Phosphorus-impaired water bodies were added to the all three data frames.

Eight separate select by location tools were used to determine how many lakes and streams that are known to have high phosphorus concentrations intersect the highly fertilized counties, high inventory cattle counties, and counties with both criteria.

Figure 1: Data flow model for Lab 4

Results

The map shows cattle inventory and fertilizer use in Wisconsin counties, as well as locations of streams and lakes with high levels of phosphorus. 

Figure 2: Map of Wisconsin counties and phosphorus-impaired rivers

A table was also created to show how the amount of streams and lake affected by high levels of phosphorus is correlated with high cattle inventory (>31000), a high proportion of fertilized acres (>161 acres per mile²), and both criteria together. As shown, cattle and fertilizer use alone increased the likelihood of a stream having high phosphorus levels, while the likelihood for counties high in both criteria was over three times that of all counties in general. This shows a significant correlation between cattle, fertilizer use, and lake and stream phosphorus levels.

Counties	Total Area (mile2)	Affected Streams	Streams/ mile2	Affected Lakes	Lakes/ mile2
All	68423.81	259	0.0037	119	0.0017
High Cattle	17136.67	146	0.0085	51	0.0030
High Fertilizer	21236.1	192	0.009	67	0.003
Cattle + Fertilizer	12485.24	131	0.011	45	0.0036

Figure 3: Streams and lakes with high phosphorus levels

Sources

2012 cattle and fertilizer data was gathered from:

https://www.nass.usda.gov/Quick_Stats/index.php

County data:

ESRI2013 database

Lake and Stream Data:

DNR database

Evaluation
I thought this was a fun lab. Although I probably could have made it easier by doing something more similar to Lab 3, land conservation is interesting to me so I pursued it. I think this made it difficult to come up with creative ways to use different tools.