To control the current water contamination epidemic, we must begin with land use reform and then move towards comprehensive land management solutions.
Freshwater resources including river systems, lakes, reservoirs, wetlands and the soils surrounding them, are being polluted at an alarming rate throughout the world. This pollution is not what we often conjure up in our minds as industrial toxics, manufacturing by-products or waste dumping. It is the by-product of landscape alteration, inadequate protective infrastructure and aging treatment systems. It involves excessive water runoff from these constructed surfaces, erosion, sedimentation, nutrients (nitrogen and phosphorus) and bacterial infestation. The cause? Agricultural food production that removes forest cover creating vast expanses of exposed sediment, fertilisers and animal waste applied to soil, inadequate human waste systems, vast areas of pavement and impervious cover, and aging or malfunctioning treatment plants. Viewed holistically, we have altered our basic hydrological cycle with these practices. We are funnelling precipitation from a natural soil infiltration to storage to purification cycle into an artificial system of dykes, levees, control ponds or pipes. These constructed systems dump excessive amounts of water, sediment and pollutants into our freshwater ecosystems worldwide. This is our current water contamination epidemic.
Agriculture and water
The developed world’s agricultural system was designed generations ago to meet food demands of an exponentially growing population. This conventional food system driven by production neglected needed safeguards to the natural systems that support it. Large swaths of self-sustaining forests were clear cut to create space needed for food production to meet high demands. Large corporations furthered the conventional agricultural system by demanding the cheapest, fastest product available in the largest quantities. Deforestation, heavy synthetic chemical use, and poor land management practices became the standard.
Agricultural use of water was problematic as well. Water used in agriculture (about 70% of the world’s water consumption) diverted and extracted to grow crops re-entered the natural system but with sediment, bacteria, and dissolved compounds. Moreover, protection of this newly exposed soil was minimal. During heavy rain events soil loss and chemical runoff began to manifest themselves into water resources. Without disturbance, natural ecosystems can nurture and repair themselves at a remarkable rate. However, the cultivation of crops and loss of intricate root system that once held soil in place has disappeared: soil now enters surface water freely, creating a very serious problem.
Sustainable farming practices helps. Use of cover crops nourish and maintain soil nutrients. Cattle farmers could transition grazing practices resembling natural grazing processes rather than overgrazing one spot for long periods. Multi-cropping practices decrease the threat of pest or disease outbreaks, in addition to improving the soil quality and root systems. To implement such programs, ample evidence justifying the benefits must be convincing. Governments need to reward farmers and market need to demand sustainable practices implementation. Such a program in the United States occurs in Maryland. They formed a Water Quality Cost-Share program awarding farmers when they plant cover crops during the winter season. If we increase a desire for organic foods, burdens on water resources can be lessened.
Human waste systems
Our human waste systems continue to put a heavy waste burden on freshwater ecosystems. These systems include wastewater treatment plants, stormwater collection sewers, grey water discharges and septic tanks. Output through these systems coupled with excessive sediment in our natural environment is producing problematic outcomes. Wastewater treatment plants are heavily regulated but built to remove human waste in the form of Biological Oxygen Demand (BOD) and pathogens. While effective in meeting these objectives, other problems are less controlled. Nutrient pollution in the form of nitrogen and phosphorus flow from these plants. The sewage sludge produced from the dewatering process is applied to agricultural fields compounding this problem. Heavy metals and the epidemic use of hormones or other pharmaceuticals flow freely from these treatment facilities into waterways. While the water appears clean emanating from these facilities, it contains multiple levels of contaminates.
However, the greater problem is the synergistic interrelationship sewage discharges produce when mixed with stormwater. Stormwater systems are built to control precipitation from constructed surfaces but have created two menacing problems. The first is a collection of surface pollutants such as oils, grease, sediment, nutrients and plastics that flow freely from constructed surfaces into streams. The second is the overabundance of water flow eroding surrounding landscapes and the streams themselves. Points of discharge, stream banks, exposed and unstable soils with sloped surfaces and deforested areas all deposit sediment into the streams. Each sediment particle is different and contains abundant surface area for the colonisation and growth of bacteria aided by nutrients and other pollutants. The clay soils found in the southern United States, central and south America, Africa and Indonesia are particularly concerning. Clay particles are flat providing an excellent colonisation surface for bacteria, stay suspended in water for long periods of time aiding long journeys of transport and are electrically charged allowing many types of attractions with pollutants. They are pollutant transport vehicles in our freshwater systems and create a figurative broth full of bacteria and contaminates.
Stormwater also transports plastic bottles and bags into wetlands, collection ponds, streams and lakes. The breakdown of plastics into chemical leachate and microplastics furthers these problems. Plastics resting in a wetland or floating on a surface photodegrade turning this waste into another transport mechanism for bacteria on its surfaces or toxicity from its materials. Just as sediment now combines with pollutants for transport, plastics serve a similar function but with the addition of a toxic leachate.
One final problem of concern is the overwhelming number of septic systems and greywater we expect to effectively treat human waste worldwide. These aging systems may be reaching threshold failure rates due to poor maintenance, neglect or inadequate installation. The biggest concern is quantification. Problem identification occurs when water contamination is detected. This sector is largely regulated by owners and not under usual public scrutiny. Repair and management are an increasingly difficult problem.
Wet and dry cycles
Low flow in streams, minimal water movement in reservoirs, dry surface conditions in wetlands and low water tables surrounding septic tanks are one condition of this problem. Low stream flow while carrying low concentrations of nutrients and sediment are highly vulnerable to bacterial contamination from human sources. We have measured extraordinarily high concentrations of E. coli in low flow streams with bacterial source tracking confirming 99.9% from human sources. We suspect septic systems coupled with illicit sewage system discharges can cause a bulk of this problem. Water flow into reservoirs reduces pollutant concentrations but loads the bottom sediments until the next precipitation event moves them downstream. Dry condition exposure of pollutants in wetlands photodegrades plastics or other waste until each becomes integrated into the problem that will manifest during the next precipitation event.
High water flow is the crescendo of contamination into the system. Heavy rain or snowmelt transports everything on the land surface directly into surface water. Exposed soil whether from recently tilled agriculture or suburban or urban construction is driven into any surface water channel available. Precipitation events now generate unprecedented concentrations of sediment and pollutants even during mild storm events. Sediment is naturally associated with nutrients and clay particulates have a strong affinity for phosphorus. Clay and phosphorus now transport with every storm event through our cities and countryside vast distances into the worlds oceans. Our stream systems are scared and unstable from deforestation and development. What sediment does not transport from the stream into the ocean during a storm event accumulates as bedload or along unstable stream banks waiting for the next storm to transport.
We now live in an era where extreme precipitation events have become more common. Warming of the climate has generated a moisture rich atmosphere that returns the moisture in differing patterns than previously understood. These events currently generate unprecedented flooding (multiple worldwide 1000 year storms have been documented in the last decade alone), landscape alteration and property destruction to the pollution problem. Conventional farming practices and stormwater management developed in an era where heavy downpours of precipitation were less frequent now contribute to the problem. The resultant bacterial, sediment and nutrient loads flowing from these storms are reaching unmanageable levels. Unstable stream bank erosion, sediment and rock flowing with dislodged vegetation threaten bridges, dams and any built structure.
While an economic benefit from both land improvements (any use other than a forest) continue to be realised, this cannot be sustained. The natural systems that support life cannot metabolise the pollutant burden they now experience. Because land is managed on a local level and contamination is better understood on a regional or national scale, we cannot expect a fundamental change in this problem without a change in how we manage land. When tax revenue is associated with land value, a local government will only encourage further development. When drinking water supply is separated from local streams or lakes, any incentive for improvement is removed. When water diversion into arid land is ignored or cattle access streams encouraged, pollution levels will continually increase. And most importantly, when those who benefit and use water upstream ignore or are oblivious to the needs of those downstream, everyone suffers.
Possibilities such as debt-for-nature swaps, preservation easements, mitigation banking, ecotourism and ecosystem services payments do provide promising hope for improvement. However, individual landowners need economic incentives to preserve forests ecosystems and we need to alter our expectations of land use. Understanding how we are interconnected in a watershed may create education and awareness and this is a start. But to control the current water contamination epidemic, we must begin with land use reform and then move towards comprehensive land management solutions. Once we all understand how each land use decision impacts the hydrological cycle and contributes to the problem, we can begin to make meaningful change.
Dr Thomas Shahady
Assistant Professor of
University of Lynchburg
+1 434 944 5684