Save Kihei

Why Is Soil Erosion Such a Big Problem?

Soil loss is a problem for pollution and for the climate. Soil takes a long time to form, hundreds and sometimes thousands of years, and can be lost in a single storm.

It takes thousands of years for rocks to break down into sand sized particles, clay takes even longer to form, plant matter takes many decades of plant life growth and decomposition to generate healthy soils. The soils we have today are a legacy of long periods of time. Soils are finite in the short term, and we are losing soil much faster then it is being replaced. The biggest contributor to soil loss is man-made agriculture, tilling and ploughing. This exposes the soils and makes the vulnerable to erosion from wind and rain.  Every year we lose billions of tons of topsoil to erosion.

Feral Ungulates: Another problem we have in Hawaii is feral ungulates. Feral Ungulates are wild animals with hooves. Examples include, Wild cattle, Pigs, Deer, and Goats. In fact all ungulates cause harm to soils, this includes all domestic horses, cattle, pigs, goats, deer, etc. 

Hooves break open the soil’s surface and destroy the groundcover. The fragile soil matrix (structure) is disturbed and erosion occurs more easily.  These hungry herbivories also eat all the plants, and remove the protective player of plants that hold the soil together. Wild pigs are especially good at digging and will make deep trenches, and goats and deer will eat every last blade of grass, plant, and even chew the bark off the trees. 

Feral ungulates have no natural predators in Hawaii (other than man). And their populations have exploded, and these animals have spread into every corner of our islands, invading every habitat and ecosystem. They also cause harm to farmer’s crops as well. 

Non point-source pollution: Most of the silt that we get in Kihei comes from upcountry, higher up in our watersheds. In particular from the “ranchlands”. There are huge, relatively dry, areas of ranchland that are dry and dusty, and are the source for the vast majority of soil that comes downhill with every heavy rain. These ranchlands have become degraded, and the native vegetation has been reduced, by cattle grazing, and by the actions of feral ungulates. Some of these upland areas are designated as “soil conservation districts”, but there doesn’t appear to be very much actual soil conservation going on.  This soil loss means diminished soil for agriculture, and less arable land area being available for our growing need to feed ourselves. 

Siltation clogs the watershed and the Wetlands: Silt and mud from the uplands has clogged many of the lower watershed features including the gulches, streambeds, flood plains, and wetlands. Kihei used to have many freshwater pools, loi kalo (taro patches), and loko i’a (fishponds), but over a hundred years of agricultural runoff and pollution have clogged them and buried them under tons of mud. A once-thriving settlement and society that lived in Kihei was eventually abandoned because their farming, aquaculture, and fishing, was so severely degraded by silt coming down from the highlands.  

Soil erosion pollutes stormwater runoff.

Soil and Silt is pollution: Lost soil also becomes a source of pollution, as it clogs streams, dams, watersheds, wetlands, rivers and eventually the ocean. Soil is a wonderful asset in its proper place, but when it gets into streams, wetlands, fishponds and the ocean it becomes very harmful. 

In Hawaii we have a big pollution problem with contaminated stormwater runoff, full of chemicals and silt (soil) entering the ocean., During “brownwater” events, massive amounts of silt are carried into the ocean where it chokes the reef, and other forms of sensitive sea life, it blocks sunlight, chokes filter feeders, disrupts the food chain, and changes the chemistry and ecology. The effects of pollution from soils in stormwater runoff, can last for many months, and and can have long-term impacts on the water quality and ocean habitats.   

Soil loss is a double-tragedy for the climate, because green areas lose their groundcover and cannot support plant life, then they get drier, which adds to warming of the local micro-climate, this can drive away clouds, and the land gets even drier as a result. The second factor is that soil is a great absorber of carbon and greenhouse gasses. Carbon dioxide (CO2) a greenhouse gas is absorbed by plants which eventually breakdown into the soil where they deposit their carbon. Soils can sequester (hold onto) huge amounts of carbon and keep it out of the atmosphere for hundreds of years.  

Clean Up After Storms: After muddy flooding events, Tons of dirt, mud, and debris have to be cleared away from roads, streams, bridges, and gulches. What doesn’t go into the ocean has to be removed, Unfortunately, most of this mud is contaminated so it cannot be reused, It has to be disposed of in the county landfill. 

For more info read this article: https://www.wri.org/insights/causes-and-effects-soil-erosion-and-how-prevent-it