Assessing the Effectiveness of Various Riparian Buffer Vegetation Types

Agricultural riparian buffer research has focused on examining water flow through native forest stands or grass filter strips (Sheridan et al. 1999), and has been conducted primarily in the Mid-Atlantic and southeastern United States (Jordan et al. 1993; Lowrance et al. 1984). Recently established riparian buffer strips, usually adjacent to crop fields, have become increasingly common in the Midwest. The climate, soils, and hydrology differ considerably between the Midwest and the eastern seaboard, thus the effectiveness of newly planted riparian buffers for filtering agricultural field runoff needs to be documented.

carboy would overflow, so the water sample was taken from the 1/64 splitter.In contrast, following a small runoff event, the 1/64 sample carboy would not yield enough volume for chemical analysis, thus the 1/16 sample would be used.For more details regarding the sampling apparatus, see Mankin et al. (2001).

Most of the runoff volume (> 92%) was returned to the buffer to continue flowing towards the stream.Sheet metal panels were inserted into the ground to prevent meandering flow paths that may have resulted in bypassing of the rear sampler.

Immediately following significant rainfall events, the water samples were retrieved and brought to the Kansas State University Agronomy Soil and Water Testing Lab.Runoff samples were analyzed for concentrations of total suspended solids (sediment), total phosphorus (and fractions), and total nitrogen (and fractions).

Surface runoff samples were collected after four storm events that occurred between June and August, 2001.Due to drought conditions in 2002, no natural runoff occurred, thus the plots were irrigated with simulated runoff three times during August and September.The simulated surface runoff was created by mixing tap water with 4 kg of field soil, 45 g of ammonium nitrate, and 6.9 g of sodium phosph te in a pickup-mounted 210 gallon tank.This mixture closely approximated the components found in the natural runoff collected the previous ye r.The vegetation was characterized with a step-point sampler for each type of buffer in September 2002.


RESULTS

All buffer vegetation types reduced runoff contaminants.The reduction in total suspended solids (TSS) concentration was highly variable for the natural runoff in 2001.The mean ranged from under 40% reduction for the Plum/Fallow plots, to over 75% reduction for the Plum/Grass plots (Figure 2).Due to the variability of the data, though, there were no statistically significant differences between the vegetation types in TSS reduction.

Reduction in TSS concentration was uniformly very high for the simulated runoff data collected in 2002, with all buffer types resulting in over 90% reduction.As expected, data were less variable for the controlled, simulated run ff, resulting in much narrower standard errors (Figure 2).

For simplicity, only the total phosphorus concentration and total nitrogen concentration will be presented.The various fractions of each nutrient were highly variable making them difficult to summarize.Trends for total phosphorus were different than observed for TSS.In 2001, all three vegetation types resulted in more than 50% reduction in concentration, again with the Plum/Fallow plot data being the most variable (Figure 3).The 2002 data showed slight differences, with means ranging from 40% for the Plum/Grass plot to almost 60% for the Fallow plot.Differences were not statistically signific

reduction in nitr
gen concentration was much less variable.Nitrogen reduction showed a different trend than TSS, and also had lower mean reductions, as would be expected for a highly soluble nutrient that is not bound to sediment (Figure 4).Plum/Fallow plots had the greatest reduction, almost 55%.Fallow plots showed less than 45% reduction in nitrogen runoff and Plum/Grass were intermediate in nitrogen reduction (Figure 4).

In 2002, nitrogen runoff reduction was significantly less than seen in 2001 for the Plum/Fallow (35%), while reductions for the other vegetation types were similar to 2001 results.The strong filtering ability of the plots with natural weedy vegetation resulting from 7 years in fallow was surprising.To better understand these results vegetation characteristics were considered.Both the fallow and the seeded zones had over 98% vegetative ground cover, although there were differences in the type of vegetation.The fallow plots were dominated by cool season grasses (50%), primarily downy brome (Bromus japonicus), which, when combined with other annuals, accounted for over of the vegetation points sampled.Conversely, the native grass area was dominated by the warm season perennial grasses (>80%) that were planted, such as Indian grass (Sorghastrum nutans) and switch grass (Panicum virgatum).The planted American plums had achieved crown closure, averaging almost 6 feet in both height and crown width, with numerous sucker sprouts appearing between the rows.


DISCUSSION


Runoff Components

The reduction in TSS concentration was highly variable with the 2001 natural runoff, but uniformly high under the 2002 simulated runoff.This may have been due to the inherent natural variability in the 2001 runoff events, and, conversely, the uniformity of contaminants and flow rate applied in the simulated runoff collected in 2002.

Total phosphorus would have a component bound to sediment.In fact, the reduction in concentration of runoff phosphorus was similar to reductions observed in TSS, when comparing buffer types and years, ranging from 40% to 60%.

Total nitrogen concentration reduction was the least of the three components measured and also had the least variability by buffer type and year, with reductions ranging from 5% to 55%.Narrow riparian buffers were less effective in filtering a soluble nutrient like nitrogen because of the relatively short residence time and the direct flow paths through the narrow buffer.


Vegetation

The 7-year-old buffer plots all had well-established vegetation.The fallow and planted plots had complete round cover, with annuals dominating the fallow plots, and warm season perennials and shrubs dominating the planted areas.The fallow plots had equal proportions of mostly annual cool and warm season grasses, which appeared to filter surface runoff quite effectively.


Future Research

The observed reductions in runoff pollutants are consistent with those reported in other studies.However, the efficiency of the fallow plots was greater than expected.These will be examined in the future to compare standing biomass and soil infiltration rates.Runoff volume data will be further analyzed to allow mass balance calculations, which will determine the

eduction
in total pollutant loading.There are other sites in Kansas currently being monitored.These include a planted prairie grass filter strip and a native, mature riparian woodland.

Figure 1 .
1
Figure 1.Overhead view of the runoff sampling apparatus in the Plum/Native Grass buffer.




.G., R.C. SCHULTZ and T.M. ISENHART.1997.How to design a riparian buffer for agricultural land.Agroforestry Notes #4.National Agroforestry Center.Lincoln, NE JORDAN, T.E., D.L. CORRELL, and D.E.WELLER.1993.Nutrient interception by a riparian forest receiving inputs from adjacent cropland.Journal of Environmental Quality 22:467-473.


Figure 4 .
4
Figure 4. Average total nitrogen concentration reduction from surface runoff achieved by three typ s of riparian buffer strip vegetation.Results from 2001 represent natural precipitation events and 2002 results represent simulated runoff.Standard error bars are shown.


Figure 2 .
2
Figure 2. Average total suspended solids (TSS) concentration reduction from surface runoff achieved by three types of riparian buffer strip vegetation.Results from 2001 represent natural precipitation events and 2002 results represent simulated runoff.Standard error bars are shown.


Figure 3 .
3
Figure 3. Average total phosphorus concentration reduction from surface runoff achieved by three types of riparian buffer strip vegetation.Results from 2001 represent natural precipitation events and 2002 results represent simulated runoff.Standard error bars are shown.

This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information is available from http://www.ksre.ksu.edu.
ACKNOWLEDGEMENTSThe EPA 319 program, via the Kansas Department of Health and Environment, Proje t 2K-049, provided partial funding for this project.Contribution no.03-305-S from the Kansas Agricultural Experimental Station.Contents of this publication may be freely reproduced for educational purposes.All other rights reserved.In each case, give credit to the author(s), name of work, Kansas State University, and the date the work was published.Kansas State University Agricultural Experiment Station and Cooperative Extension Service Manhattan, Kansas 66506 SRL 137 March 2003 It is the policy of Kansas State University Agricultural Experiment Station and Cooperative Extension Service that all persons shall have equal opportunity and access to its educational programs, services, activities, and materials without regard to race, color, religion, national origin, sex, age, or disability.Kansas State University is an equal opportunity organization.These materials may be available in alternative formats.Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended.Kansas State University, County Extension Councils, Extension Di

ited States Depart
ent of Agriculture Cooperating, Marc A. Johnson, Director.1000 This publication was produced by the Department of Communication, K-State Research and Extension.
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