From: http://www.unwater.org/statistics/statistics-detail/en/c/211798/Increases in fertilizer use for food production suggest a 10-20% global increase in river nitrogen pollution
Projected increases in fertilizer use for food production and in wastewater effluents over the next three decades suggest there will be a 10-20 percent global increase in river nitrogen flows to coastal ecosystems.
Due to fertile land and access to water, agriculture has long developed near rivers, lakes, and has cleared forests and wetlands for crops. Below is a list that describes some of the biggest concerns in agriculture and how such actions have degraded the river system and environment. Note that we like agriculture, everyone needs agriculture - it is where we get our food. Many farmers we know deeply care about their land, the environment, and pursue many ways to improve their practices. What we aim for in this content is education, that there are impacts of our past methods that need to be rectified today as well as a push to promote the current shift to new technologies for a sustainable future.
Development in the floodplain
Rivers occasionally flood, and with the high water they bring new sediment, move old sediment, deliver nutrients, and often deposit vegetation and seeds to the floodplain as well as remove vegetation. These complex relationships between flood events and the ecosystems has been researched for decades, but the systems and mechanics are so complex and dynamic that they are still not well understood. However, what is understood is that when developments, like agriculture, impede the floodplain and alter the landscape, the interrupt these complex systems, and often limit the water’s inundation and flow pattern, which causes a disconnect in the floodplain and reduced habitat. By pushing more flow into a river channel, the depth and velocity increases, which inturn causes greater erosion and leads to channel incision that causes increased erosion (resulting in higher water pollution), lower channels (resulting in lower water table), and the reduction in active floodplain also causes reduced area for habitats for both land and water fauna and flora.
When agriculture removes vegetation and plants crops, two problems arise. First, the soil is tilled which reduces the overall vegetation density and root mass that binds the soil. This loose soil is highly erodible, and with less vegetation cover it is easily transported into the nearby waterways through ground water runoff. Secondly, in the application of pesticides, herbicides, and fertilizers and the over abundant irrigation washes these nutrients and chemicals into the nearby waterways, causing significant water pollution and unsuitable habitats.
Worldwide, excessive amounts of nutrients (eutrophication) has been identified as the most widespread, costly, and challenging contributor to water quality issues. Primarily, these nutrients are nitrogen and phosphorus, which occur naturally in nature, but excessive amounts enter our waterway from agriculture, storm water, waste water, and residential areas. However, agriculture is the primary source (48% of water stream and river pollution in the United States; and 50-80% of nitrogen comes from agriculture in the EU).
Nutrient water pollution causes an increase the growth and presence of both good and bad algae. While some algae blooms of ‘good’ algae can actually increase the amount of available food for aquatic species, there are a small percentage of algae that produce powerful toxins that can kill plants and animals. Regardless of the good or the bad, both cause ugly scenarios when the algae dies and decomposes because it reduces the amount of oxygen in the water which causes animals to have to leave or die. Algae blooms occur both in freshwater and marine environments, and are occurring at an alarming rate around the world (http://www.epa.gov/nutrientpollution/harmful-algal-blooms) (need a map).
To maintain the land, irrigation draws from the rivers, lakes, and ground water. However, most of todays irrigation uses inefficient water technology to pump, pipe, and spray the crops. This overuse of water causes unnecsseary ground water runoff that transports the unnecessary large amount of nutrients to the waterways. Further, the irrigation reduces the volume in the river, which thereby reduces the available and suitable habitats for fish, further disconnects the active floodplain, and reduces ground water levels. Irrisponsible ground water extraction for irrigation also decreases the water table, which responds by lowering the nearby waterways. Thus all actions in agriculture have a reaction that make future practices more difficult.
Finally, agriculture has been both an direct and indirect reason that many grade control structures have been constructed. While grade controls have been shown to reduce channel incision and bank erosion, some studies have shown grade control to exacerbate the conditions (Simon and Darby), reduce sediment transport, encourage sediment homogenization, prevent fish passage, and allow vegetation to encrouace the active channel and thus reduce habitat and increase flood inundation levels.
When agricultural land replaces floodplains, wetlands, and forests, it also changes the ecosystem. This includes both the available and suitable habitat for fauna and flora, but also changes how the land and environment behave. Floodplains, wetlands, and forests naturally store large amounts of water, increase the water table, trap nutrients, and reduce surface water runoff as well as provide a rich ecosystem for nature. In addition to the above promblems of pollution and runoff, reduced floodplain connections, and reduced ground water, removing these natural lands causes higher temperatures, have little or no ability to store long-term carbon, and can even reduce the amount of precipitation the area receives ().
As we have shown, agriculture has huge impacts on water. Now consider that agriculture consumes 69% of the world’s freshwater (US, EU, AUS, NZ), and that the world’s 100 largest cities get their water from watersheds that are covered by 50% or more agricultural land. Unfortunately, agriculture is one of the leading causes of nutrient pollution from non-point source pollution, which is the world’s most widespread, expensive, and challenging contributors to poor water quality. However, while it is easy to point the finger at agriculture, we should consider that agriculture also suffers from water pollution and overuse. This makes the time ripe for change, plus most many methods that will ultimately reduce the pollution and overuse of water will also reduce agriculture expenses and many have the potential to improve annual crop yields.