We often think of soil health and water security as distinct conservation issues, but in fact they are inseparable. A new study from The Nature Conservancy (TNC) underscores how good soil management is not only foundational to safeguarding water supplies, but also generates additional benefits on local to global scales.
Locally, good soil health benefits farmers growing crops, and the often hidden species living underground. Regionally, good soil health means less sediment entering rivers, whose water is essential to downstream communities and industries, and to economically-important coastal zones. Healthy soil also promotes the infiltration of water into the ground, which can mean more downstream water available during dry times and less flash flooding during storms. Globally, good soil health means greater long-term agricultural productivity for the world’s growing population and significant avoidance of carbon loss to the atmosphere that would otherwise contribute to climate change.
Plants and the soils in which they grow collect, store and filter our water. However, for the most part we’re not managing our soils and lands well. Deforestation, poor agricultural practices and other land uses have led to moderate to high degradation of 40 percent of the land within the world’s urban source watersheds—a worrying statistic.
In the past, water quality and quantity challenges have typically been met by building more aqueducts, reservoirs and treatment plants. But this solution isn’t sustainable; we can’t keep building our way out of a water crisis, we need to protect its source. So, where to next?
Investing in Nature
Nature-based solutions for water security are also, in many cases, solutions for soil health. Four out of five of the more than 4,000 cities studied in the new report could reduce sediment and nutrients in their water by committing to the reforestation of pastureland, forest protection and the planting of trees and cover crops in the farmlands of their source watersheds. All of these activities can benefit soil health. Cover crops in particular are a soil management tool, designed to decrease soil erosion and improve soil fertility on agricultural lands, in addition to inhibiting weeds, pests and diseases, and safeguarding soil biodiversity.
The benefits of good land management are nearly universal. Eighty-three percent of urban source watershed areas are predicted to experience increased erosion by mid-century due to climate change. Good land management means less erosion—both now and in the future. And good land management to protect downstream water supplies for cities has the added benefits of helping farmers, species and the global community.
Good soil management is also an unsung hero in the climate story. Soil contains two to three times more carbon than the atmosphere. This means that small changes in soil carbon—either improvement or deterioration—can have a big impact on atmospheric carbon.
In lay terms, increasing or maintaining soil organic carbon has two benefits. In addition to helping to mitigate climate change, it improves soil health and fertility. In turn, many management practices that increase soil organic carbon also improve crop and pasture yields. Farms with good soil management may be more resilient to climate change impacts like drought, and small-scale farmers and farming communities may have greater resilience as a result. In aggregate on the global scale, well-managed agricultural lands can make a meaningful contribution to mitigating climate change, creating a virtuous circle.
Reforestation, forest protection and agricultural best management practices like cover crops, if implemented fully across the world’s urban source watersheds, could store or capture up to 10 gigatonnes of CO2 annually. This is approximately equal to humanity’s combined emissions from burning oil globally (10.82 GtCO2e in 2013, IEA)—a figure worth noting. Source water protection, then, is a vehicle not only for water security, but for mitigating and adapting to climate change, protecting biodiversity, and improving the health and well-being of both upstream and downstream communities. And much of this relates to our soil.
Getting It Right
Over 35 percent of the planet’s ice-free surface has been cleared of natural vegetation to grow crops or graze livestock, exposing it to sharp increases in erosion and steep losses in soil organic carbon, soil nutrients, and biodiversity. We need to get this right, and in recent decades we haven’t. A new paper in Nature confirms that climate change will accelerate the decomposition of soil organic carbon, releasing large amounts of CO2 into the atmosphere, which we can ill afford.
In many geographic regions, we know what needs to be done for soil health. Many interventions are practical: conservation tillage, which entails reducing plowing and leaving the crop residue on fields before and after planting the next crop; cover cropping, which entails planting legumes and other plants that keep soil protected and provide biomass to soil to rebuild organic matter; organic matter recycling and use of perennial crops, which are alive year-round and are harvested multiple times before dying. There are more. Perhaps less well understood is that we need a combination of these interventions, applied across very large areas of agricultural lands.
TNC estimates that US$42 billion to US$48 billion annually would be required to achieve a 10 percent reduction of sediment and nutrients in 90 percent of our urban source watersheds. With this level of funding, we could improve water security for at least 1.4 billion people by first focusing on the most cost-effective watersheds for water security purposes.
Source water protection is in many ways just good land stewardship, and that includes stewardship of our soil resources.
The beauty of source water protection, when implemented in partnership with farmers and other land stewards, is that its benefits can encompass and go well beyond water security, creating a diverse constituency that links people working the soil with those downstream and across the globe.
Photo Credit: USDA-NRCS