Nested hierarchy theory advances the idea that rivers have a fractal dimension where processes at the catchment scale (>1 km) control processes at the reach or mesoscale (100 m) and microscale (1 - 10 m). Largely absent from this work is a mesoscale link to the larger and smaller scales. We used stream alteration classifications to provide this link. We used orthophotographs, land cover, and LiDAR derived terrain models to classify stream alterations within four watersheds. We compared phosphorus point data with watershed, sub-watershed, and 100-meter buffers around the point data. In the predominately urban watershed, the 100 m buffer scale correlated better with phosphorus levels. In the predominately agricultural watershed, the sub-watershed scale correlated with phosphorus levels better. We found adding the classification of the stream alteration type clarified anomalously low phosphorus levels.
Nested hierarchy theory (NHT) advances the idea that rivers have a fractal dimension where processes at the larger watershed scale (>102 km) and sub-watershed (>1 km) control processes at the reach or mesoscale (100 m) and microscale (10 - 1 m) [
The Frissell et al., 1986 NHT provided a conceptual framework for abiotic and biotic projects designs, data collection and analysis. The original RCC developed from geomorphic models of rivers having “dynamic equilibrium” [
NHT assumes large scale processes within a river influence smaller scale processes. Of interest is landuse’s role at the watershed and reach scale, particularly agriculture, urban, forest, and wetland. In general water quality samples usually have lower sediment and/or pollutants in regions with lower percentages of agriculture and urban. Prior studies have determined that human alteration to the landscape yields a response across many scales [
The net result of 30 years of projects investigating watershed scales and their relationship to landuse has not resulted in a consensus [
Studies investigating the optimal scale of landuse to predict water quality have yielded opposing results. Research in a wide variety of landuses has found that watershed scale landuse factors may not be strongly correlated with water quality indicators at the reach or microhabitat scale. Researchers have found that riparian vegetation, bank condition, and landuse directly adjacent to the site are better indicators of water quality [
Other studies suggest that watershed scale factors play an important role in understanding the smaller scales [
Some papers suggest that the confounding factor reducing the efficacy of a landuse evaluation of water quality and habitat is the location of environmental factors [
In a comprehensive review of the landscapes and their interactions with streams, Allen, 2004 identifies and summarizes six principle environmental factors that affect rivers: 1) sedimentation; 2) nutrient enrichment; 3) contaminant pollution; 4) hydrologic alteration; 5) riparian clearing and opening; and 6) loss of large woody debris [
Management of watersheds, especially those impacted by anthropogenic landuse (e.g. agricultural and urban) is driven by a need to maintain water quality at set levels and to manage sampling costs. Predictive water quality models using landuse characteristics at the watershed scale often fail to target specific regions within the watershed requiring remediation [
In this paper, we identify and classify hydraulic alterations using spatial data. Our hypothesis is twofold. First, we expect a higher percentage of altered waterways will be found in watersheds with higher amounts of anthropogenic landuse; and second, that water sampling points will correlate best with landuse buffers from the immediate location. We also expect that anomalously low or high readings will be better accounted for by their hydraulic classification. We define our research scales as follows: large scale (watersheds: approximately 130 km2), intermediate scales or mesoscales (sub-watershed (10 - 0.05) km2 and stream segments 10 km), and microscale (100-meter buffers around water quality sampling points, 0.1 km2).
Site DescriptionThe selected hydrologic unit code 12 (HUC12) watersheds reside in four regionally different locations and have varying landuse in Wisconsin: Swamp Creek-north central, West Fork Knapp Creek-south central, Bass-Stevens Creek-south central, and Milwaukee River-south east (
Fork Knapp Creek is located in Crawford and Richland counties in the Driftless Area. It has a drainage area of 47.9 square km with a total of 75 stream km. West Fork Knapp Creek, a cold headwater stream of the Wisconsin River, is dominated by forest landuse. Bass-Stevens Creek watershed is located in Rock County and has intensive agricultural activity; 70 percent of the total area. Bass-Stevens Creek is classified as a warm headwater stream to Rock River watershed and was placed under Total Maximum Daily Load (TMDL) study in 2011 [
Data used for classification of altered hydrology came from state and federal sources. An existing geospatial stream vector file from the WDNR [
Prior to determining altered hydrology, fields were populated in the stream vector feature class table. Altered water course type (AWC-type) with domains: (1) Altered, (2) Natural, (3) Impounded, and (4) No Definable Channel. Sinuosity was also added and calculated using the ArcPy Sinuosity tool (ArcGIS ver 10.2). This takes the distance along all vertices on the stream channel from start point to endpoint and divides by the straight-line distance between the two points. A sinuosity value approaching zero represents more sinuous while a value approaching one is less sinuous or straighter. Each stream segment was assessed separately. If a stream segment lies in two different classifications, the segment would be split and classified appropriately. For example, a long stream segment that crossed into an agriculturally dominated area and became less sinuous would be classified as altered. If the other portion of the same segment were more sinuous and resided in a forest-dominated area with no apparent anthropogenic changes, this portion would be classified as natural. Classification of altered hydrology followed the Minnesota Geospatial Information Office (MnGeo) for altered watercourse framework [
In order to classify a stream reach as altered, adjacency to agricultural operations, sinuosity, and general anthropogenic alterations were assessed. Each stream flagged as potentially altered was compared to certain acquired spatial layers. Recent 2013 aerial imagery was compared with the original 24 K stream’s digital raster graphic (DRG). If drainage pattern was similar, LiDAR hill shade and digital elevation model data were compared with the streams. Lastly, 2013 and 1938 aerial imagery along with LiDAR data were compared. Stream channelization not displayed in the DRG but apparent in recently acquired LiDAR was considered altered.
Historic and recent aerial imagery comparisons also aided in displaying even the smallest alterations. Streams that were previously natural may have been altered through ditching. A strong predictor of ditching is a stream’s adjacency to agricultural landuse and changes in sinuosity. The presence of any linear feature or structure that represents human interaction with nearby hydrology results in a stream classification of altered. Bank stabilization, levee construction, or cement structures constraining flow will alter a stream’s natural course and are examples of types stream segments that would be considered altered.
Agricultural landuse is associated with ditching, draining, and channel straightening, so stream segments within a prominently agricultural area with low sinuosity were examined closely (
prior aerial imagery are unaltered even though increased agriculture is present. We determined if channel sinuosity is retained and there are no structures or evident changes, the stream segment is classified as natural. Stream segments that closely border a road or other obstructions such as water and sediment control basins are classified as altered. Stream segments with forested regions around them but are adjacent to roads are also considered altered because roads change the channel’s natural flow path (
Sinuosity in headwater streams was less important in steeper gradients. Headwater streams in high relief regions do not have the hydraulic capability of creating meandering channels. Stream segments adjacent to an expanse of forest and distant from agricultural impacts and any manmade structures were indefinitely classified as natural (
Wetlands information was accessed by NWI wetlands inventory and was draped over the stream layer. Noticeable wetlands that surround a stream and are considered functional were classified as natural. However, indications of a “dried-up” wetland are considered altered [
Water body features that interrupt river systems are often anthropogenic. Using the Wisconsin lakes data and prior aerial imagery, impounded watercourses were identified. Water body features that were not observed in 1938 aerial imagery but were found
in 2013 aerial imagery indicate an anthropogenic structure (
Streams delineated from historic maps and aerial imagery can change course or disappear altogether over time. It is often hard to define any path that these streams take which in turn makes them harder to classify. Stream vectors that cross tillage land with no distinct flow path are considered to have no definable channel. Even if a stream looks distinct and well definable from an aerial imageries view, analyzing LiDAR data can assist in determining if a watercourse exists. The non-existent stream that is not definable through LiDAR draped over hill shade is classified as no definable channel. Another indicator of a lack of definable channel is a stream’s path in relation to tillage. If a stream’s path is perpendicular to tillage lines, the effective drainage direction of that reach is destroyed. A path is no longer definable from either aerial imagery or LiDAR.
Water quality sampling data were obtained from the WDNR sampling and volunteer monitoring program and Environmental Protection Agency (EPA) Storage and Retrieval and Water Quality Exchange (STORET) and combined into a statewide database [
We divided Milwaukee and Bass-Stevens watersheds into sub-watersheds using the sampling points as outlets. The watersheds were delineated using Arc Map 10.2’s hydrology toolbox. For Milwaukee River, the sub-watersheds ranged from 8 to 104 km2. For Bass-Stevens Creek watershed, the sub-watersheds ranged from 0.02 to 5.6 km2. We designate these as “watershed scale”. We also used the Arc Map 10.2’s buffer tool to create a 100 m buffer around each point. We designate these as “reach” scale. For each sub-watershed and 100 m buffer, we extracted landuse [
We compared total phosphorus from the point data to major landuse within the sub- watersheds and the 100 m buffers. The Mann Kendall trend test, a nonparametric statistical hypothesis, was used to evaluate the significance of upward or downward
monotonic trends using Minitab 17. Descriptions of the Mann Kendall trend test are well cited in published research literature [
USGS 2011 and USDA Cropland 2014 data percentages were extracted for each watershed (
Land Cover | West Fork Knapp Creek | Bass-Stevens Creek | Swamp Creek | Milwaukee River |
---|---|---|---|---|
Developed | 3.8 | 5.6 | 1.9 | 79.9 |
Barren Land | 0.0 | 0.0 | 0.0 | 0.1 |
Forest | 63.9 | 3.4 | 49.4 | 5.5 |
Herbaceous/Shrub | 14.3 | 22.5 | 7.6 | 2.5 |
Cultivated Crops | 18.0 | 67.8 | 0.1 | 4.4 |
Wetlands | 0.1 | 0.7 | 39.0 | 6.0 |
Water | 0.0 | 0.0 | 2.1 | 1.6 |
cent) than the other three watersheds. Specifically corn and soybean make up the highest percentage of the cultivated crop classification in Bass-Stevens Creek (58%). Most of the streams in Bass-Stevens Creek were categorized as impounded (68 percent). West
Fork Knapp Creek watershed has greater deciduous forest cover (63 percent) than the other watersheds based on USDA Cropland 2014 [
Swamp Creek, which is mainly deciduous forest and woody wetland land cover had the highest percent of natural streams (96 percent). A small percentage of Swamp Creek’s hydrology (4 percent) were classified as impounded. The Milwaukee River has 80 percent of its landuse as urban developed. The watershed contained the most diverse waterways with 34 percent of classified as altered, 32 percent classified as natural, 20 percent classified as impounded, and 14 percent classified as no definable channel.
As summarized in the methods section, the Milwaukee River (n = 25) and Bass-Stevens Creek (n = 8) watershed has several sampling points with total phosphorus (mg/L) data collected mostly during the last five years. The average of the data points for the Milwaukee River total phosphorus is 0.2 with a range of 0.09 to 0.47 mg/L. The average for the Bass-Stevens watershed was 0.094 with a range of 0.04 to 0.16 mg/L.
The twenty-five sub-watersheds of the Milwaukee River watershed’s landuse (ranging in drainage area 8 - 104 km2) were relatively homogenous. Most of the sub-watersheds had over 80 percent developed landuse, which was similar to the main watershed. The landuse range percentages for the sub-watersheds are as follows: developed landuse (40 - 100), agricultural ranged (0 - 46), forest (0 - 11), and wetland (0 - 10). The largest landuse ranges, developed and agricultural, were relatively homogenous with averages of 77 and 8 percent, respectively. One of the sub-watersheds had a very high agricultural landuse (46 percent) and low developed (40 percent), but the majority of the sub- watersheds had less than 10 percent agricultural landuse and over 75 percent developed. Sub-watershed landuse was homogenous, so it was not used to compare total phosphorus values to percent landuse in any of the other categories with the exception of we Statistical tests confirmed visual assessment of the data revealing no statistically significant results in comparing sub-watershed landuse percentages to total phosphorus levels.
The eight sub-watersheds of Bass-Stevens Creek (ranging in drainage area 1.2 to 5.6 km2) were also similar to the main watershed landuse and relatively homogenous. Developed landuse ranged from 0 - 4 percent with an average of 3 percent. Forest landuse ranged from 0 - 3.5 percent with an average of 1.6 percent. Wetlands ranged from 0 - 4 percent with an average of 1 percent. Cultivated crop landuse in this watershed did have a wider range from 32 to 100 percent with an average of 72 percent within the sub-watersheds. Statistical tests confirmed visual assessment of the data revealing no statistically significant results in comparing sub-watershed landuse percentages total phosphorus levels, with the exception of cultivated crops. The Mann Kendall trend test could not be used due to insufficient number of points (ten or more points are required). In
For the Milwaukee River watershed, the 100-m buffers yielded a different story, perhaps in part due to a much higher heterogeneity, especially in the developed landuse percent than the sub-watershed. The landuse ranges percentages for the 100-m buffers are as
follows: developed landuse (0 - 100), agricultural ranged (0 - 5), forest (0 - 30), and wetland (0 - 65). Developed landuse percent compared to average total phosphorus (mg/l), shows a positive correlation up until 80 percent developed landuse
Around approximately 80 percent developed landuse and higher, the water quality sampling points show anomalously lower levels of total phosphorus
phosphorus versus 100-m buffer developed landuse percent has a correlation coefficient of 0.61, which indicates that approximately 60 percent of the linear model presented is explained. Results of the Mann Kendall for the Milwaukee River 100-m buffer indicate that there is a significant positive trend (p < 0.004) for phosphorus levels of the 100-m buffer developed landuse from 0 - 80 percent. For the entire range of 100-m buffer developed landuse (0 - 100 percent), there is no significant trend (p > 0.1).
The Bass-Stevens watershed 100-m buffer also yields different results from the sub- watershed scale. The 100-m buffer zones have higher heterogeneity in many of the landuse categories. Developed landuse ranges from 17 to 69 percent with an average of 28 percent. Hay and pasture landuse ranges from 0 to 45 percent with an average of 14 percent, and forest ranges from 0 to 6 percent with an average of 3 percent, but both categories have five of the eight points with values of zero for the landuse percent. Cultivated crops landuse ranges from 25 to 82 percent with an average of 67 percent, and this was the only landuse category with enough heterogeneity to evaluate its relationship to total phosphorus. The correlation coefficient between total phosphorus versus 100-m buffer cultivated crops was 0.001, which indicates a model that has less 1 percent of the variance explained. It does not model the observed values and is statistically insignificant. As mentioned, the Mann Kendall trend test could not be used due to insufficient number of points (ten or more points are required).
Overall, the more anthropogenic landuse found within a watershed, the higher the amount of altered waterway classification (
The Milwaukee River’s is a predominately urban watershed. The 100-m buffer developed landuse percent ranged from 0 - 100 percent. The eleven points in the range from 80 - 100 percent developed do not follow the increasing total phosphorus trend found in the other data points (between 0 - 80 percent developed). Six of those eleven points are on first order streams near the headwaters of the watershed (see
In the case of Bass-Stevens Creek, landuse within the 100-m buffer point does not have a statistically significant relationship with total phosphorus. Rather, the sub-wat- ershed scale correlates better than the 100-meter buffer scale for cultivated crops versus total phosphorus. This difference from the Milwaukee River may be for several reasons. The sub-watersheds for Bass-Stevens Creek are smaller, where the largest sub-wate- rshed (5.6 km2) was smaller than all of the Milwaukee River sub-watersheds. Unlike the Milwaukee River, Bass Steven’s landuse is more homogenous. In Bass-Stevens Creek 90 percent of the landuse is associated with agriculture (where pasture and hay are considered agricultural landuse) while the Milwaukee River watershed is 80 percent developed (including low intensity development). Another difference between the two watersheds is the type of hydrologic classification. Bass-Stevens Creek is more homogenous based on classification, with approximately 70 percent altered and only 5 percent natural. The Milwaukee River has over 30 percent of its streams classified as natural. Finally, all of the Bass-Stevens Creek STORET sampling points (n = 8) were located onhydrologically altered waterways and several (n = 5) of Milwaukee River were on natural streams.
Altered waterways are highly correlated with watersheds that have more anthropogenic landuse. While this result confirms what is well documented in the literature, it also gives us additional information as to why larger scales (sub-watershed) landuse may not correlate well with water quality data such as phosphorus levels. In this paper, we found the Milwaukee River reach scale (100-m buffer) had a statically significant relationship between the dominant landuse (urban) and STORET phosphorus point data. In Stevens-Bass Creek, the sub-watershed scale showed a statistically significant relationship between the dominant landuse (agriculture) and phosphorus. Other studies have shown either a mix of scales to better correlate with water quality indicators [
The Bass-Stevens Creek watershed finding of catchment scale landuse having a higher correlation to water quality indicators is similar to Silva and Williams (2013) who compared two scales (100-m buffer zones and whole catchment scale (sub-watershed) in a 332 km watershed of diverse landuse (forest, agricultural, and urban) [
Esselman and Allan (2010) also note that the reach scale is still important and explained about 30 - 50 percent of the variance within their models [
In this study we examined two watersheds with significant anthropogenic impacts to both landuse and the stream channels themselves, but we found differences in which scale explained the total phosphorus levels better. Bass-Stevens Creek and the Milwaukee River both have over 80 percent landuse that is associated with human alteration, but the Milwaukee River has 30 percent of its channels which are considered natural, by comparison to Bass-Stevens Creek, which has nearly all channels altered. In contrast to the Milwaukee River, all sampling points for Bass-Stevens were on the same type of stream alteration. The homogeneity of the Milwaukee River data combined with the observation that lower phosphorus levels were found along the natural portions of the river may suggest that alteration type is a factor that should be considered.
This study uses remote sensing and filtering techniques to identify stream alterations. Without using a GIS method developed by MNGeo (2011) [
The authors are grateful to Matt Diebel’s help in retrieving the water quality data. M.J thanks Katherine Logan, Ashley Ignatius, Kelsey Budahn, Justin Watkins, Joe Magee, Bill Thompson, Casey Scott, Tiffany Schauls, Shaina Keseley, Ben Roush, Jen Ender, and Susanne Meader. The authors are also grateful to the University of Wisconsin-Stevens Point for the grant for a publication grant.
Johnson, M. and Clancy, K. (2016) Linking Watershed Scales through Altered Waterways. Journal of Wa- ter Resource and Protection, 8, 885-904. http://dx.doi.org/10.4236/jwarp.2016.810073