# Presentation: 264322

## Evaluation of Two GIS Techniques to Create Aquatic Habitat Layers in Small South Dakota Impoundments

_**Introduction**_
**Geographic Information Systems (GIS) have been, and are being,    used to create aquatic habitat layers (e.g., vegetation and substrate)  **
**There are several techniques that can be used to create habitat layers **
**There is very little published information concerning which technique is most realistic and accurate for creating small impoundment habitat**** ****layers****  **

_**Methods**_
_**Data Collection**_
**Eight small (24-64 ha) South Dakota impoundments**
**Substrate and aquatic vegetation geo-referenced at 130 random locations**
**Aquatic emergent vegetation borders geo-referenced **
_**Objective 1:  Accuracy Assessment**_
**Step 1: Three replicates of 100 locations randomly selected from ****	****   empirical 130**
**Step 2: Generate three habitat layers (i.e., substrate, ****	****	****   vegetation without known areas of emergent vegetation, ****	****   and vegetation with known areas of emergent vegetation) ****	****   using ArcView GIS 3.2**
** ****	**** ****Technique 1. Thiessen polygon**
**	****	****	****   ****Definition:  Unknown areas are estimated by ****	****	****	****	****	****	**** creating regions that bisect the ****	****	****	****	****	****	**** known points**
**	**** ****Technique 2. Inverse distance weighted (IDW) interpolation **
**	****	****	****   ****Definition:  Unknown cell values are estimated ****	****	****	****	****	****	**** from their spatial proximity to ****	****	****	****	****	****	**** known values (i.e., 12 nearest ****	****	****	****	****	****	**** neighbors) and linearly weighted ****	****	****	****	****	****      (i.e., power = 2)**
**	****	****	****	****	****   ****	**** *****Assumes continuous data**
**Step 3: O****verlay the 30 remaining points on the layer and ****	****   ****	****   determine how many points were correctly classified**** **
**Step 4: Statistically test for differences in mean accuracy ****	****  ****	****   between the two techniques using a paired t-test with ****	****   alpha = 0.05 and Bonferroni adjusted probabilities****	****	****   (data met parametric assumptions)**
_**Objective 2: Habitat Characteristics and GIS Accuracy**_
**Step 1: Calculate percent coverage of each substrate type based ****	****   on 130 empirical locations**
**        ****Calculate percent coverage of each vegetation type based ****	****   on 130 empirical locations**
**        ****Calculate impoundment morphometric characteristics ****	**
**Step 2: Statistically test for relationships between habitat ****	****   characteristics and GIS layer accuracy using the Pearson ****	****   ****product moment correlation coefficient with alpha = 0.05 ****	****   ****and Bonferroni adjusted probabilities**** ****	****	****	****	****   (data met parametric assumptions)**** **
**	**

_**Objectives**_
**To evaluate the use and determine the accuracy associated with two GIS layer creation techniques in small South Dakota impoundments**
**To determine what factors influence GIS layer accuracies in small South Dakota impoundments**

_**Summary and Recommendations**_

_**Results: Objective 1**_

**The points (N=100) located on each habitat layer below were used to create that layer**

**Substrate Layer (Potts Dam)**

**Vegetation Layer (Potts Dam)**

**The detritus area represents an error of commission created by using discrete data in the IDW interpolation**

**The detritus area is removed and coded to the most likely category that would occur at that location (i.e., silt/clay)**

**Mean accuracy for both substrate and aquatic vegetation layers with known emergent vegetation areas created using IDW interpolation appears to be influenced more by ****the frequency distribution of points across layer categories, rather than impoundment surface area or shoreline development index ****(SDI = shoreline length/2*(sqrt(surface area*********)))**
**  **

-  **IDW interpolation appears to be better suited for                                                  ****	****creating aquatic habitat layers**
**BUT......... possible human bias is included when errors of commission are ‘cleaned’**
**ALSO......... this study only used IDW interpolation with one setting (i.e., 12 nearest neighbors and power = 2); other settings could possibly result in either higher or lower accuracies**
** ****100 random locations within each impoundment appear to ****	****be sufficient for creating habitat layers using IDW ****	****interpolation with reasonable accuracy (commonly > 70%)**
**Vegetation layer accuracy increases when known areas are included**
**Layer accuracy cannot be predicted without prior field investigation (i.e., estimate of percent coverage of habitat types)**
**Increase number of sample locations if complex habitat types exist or if accuracy is not as high as desired**

**Stephen K. Wilson and David W. Willis**
** ****Department of Wildlife and Fisheries Sciences, South Dakota State University **

_**For all eight study impoundments:**_
**Thiessen polygon without known area accuracy                         =     **
**Thiessen polygon with known area accuracy**
**P = 0.065**
** ****AND**
**Thiessen polygon without known area accuracy**
****
**IDW interpolation with known area accuracy**
**P = 0.015**
**AND**
**Thiessen polygon with known area accuracy                         ******** **
**  ****IDW interpolation with known area accuracy **
**P = 0.005**
_**IDW technique again had highest accuracy**_

_**For all eight study impoundments:**_
**Thiessen polygon accuracy                         ********                                           Modified IDW interpolation accuracy**
**P = 0.0006**
_**Thiessen polygon accuracy **_
_**consistently lower**_

_**Results: Objective 2 (eight study impoundments)**_

**Evaluation of Two GIS Techniques to Create Aquatic Habitat Layers in Small South Dakota Impoundments**

**Brian Heikes**