Editor’s note: This article was written by Elizabeth Creech, Natural Resources Inventory and Assessment, on Feb. 1.
Joseph Prenger is the wetlands lead for the Conservation Effects Assessment Project (CEAP), an effort led by USDA’s Natural Resources Conservation Service (NRCS) to quantify the effects of voluntary conservation across the nation’s working lands. In this Ask the Expert, Prenger answers questions about new CEAP findings on the capacity of wetlands to capture and store nutrients from cropland fields, associated water quality benefits, and NRCS resources to support wetlands on private and Tribal lands.
USDA: Let’s start with the basics: What are wetlands, and how do they improve local water quality?
PRENGER: Wetlands occur where water covers or is present near the soil’s surface, either seasonally or year-round. Wetlands in agricultural settings may capture and store sediment and nutrients from the surrounding environment, reduce flooding, contribute to climate change mitigation by serving as a carbon sink, increase biodiversity, and provide wildlife habitat.
This nutrient capture and storage component is key for local water quality. We know nutrients, namely nitrogen and phosphorus, support healthy, productive crops. When nutrients are lost from cropland fields and enter local water bodies; however, they may contribute to harmful algal blooms and hypoxic or low oxygen zones, and compromise water quality.
A recent CEAP report highlighted an increase in both nitrogen and phosphorus lost from cropland fields over a ten-year period. Based on these findings, NRCS is focusing on efforts to help farmers and other land managers save money and protect water quality with SMART Nutrient Management.
Supporting farmers in making targeted, site-specific decisions to effectively manage nutrients is critical. It’s very difficult to achieve 100% crop uptake and 0% nutrient loss, though, even with strong planning. We need SMART Nutrient Management to reduce the amount of nutrients lost from cropland fields, plus a way to capture and store those nutrients that are lost before they reach local water bodies. Wetlands in agricultural landscapes have the potential to serve this second function, particularly when restored or constructed with this goal in mind.
USDA: You recently published findings on increasing the water quality benefits of agricultural wetlands. What are the key takeaways for farmers?
PRENGER: We published a new Conservation Insight on this topic in January 2023. Findings pull from a literature review of studies reporting field measurements for prairie-pothole wetlands found throughout parts of Iowa, Minnesota, Montana, North Dakota, and South Dakota. In short:
Nitrogen retention by these wetlands ranged from 15% to 100%, and phosphorus retention ranged from 0% to 100%.
These are large ranges. An individual wetland’s effectiveness in capturing and storing nutrients depended largely on upland management practices.
Accumulation of sediment from agricultural fields, for instance, may eventually lead to infilling of wetlands and associated reductions in water storage capacity. A buffer between cultivated cropland and the adjacent wetland — such as a grass filter strip — may reduce this sedimentation and deliver significant improvements to water storage and nutrient capture.
Here is the bottom line for farmers — when strategically integrated in operation-wide conservation planning, wetlands can offer a suite of benefits. The key is to plan them as part of an overall strategy that carefully manages the contributing areas to reduce contaminant loading and preserve wetland functions. Wetlands can significantly reduce nutrient loss to waterways, supporting water quality goals both locally and in terminal water bodies like the Great Lakes or Gulf of Mexico.
In addition, wetlands can help reduce flooding and recharge groundwater supplies, serve as a carbon sink, increase biodiversity and provide wildlife habitat.
