Most N occurs naturally as a harmless gas that makes up around 78% of our atmosphere. However, this gas is not available to most living things. This leads to a scarcity of available N in most ecosystems making it a “limiting nutrient”. Basically, of all the building blocks for life in an ecosystem, like carbon and oxygen, the least available is N, which dictates how productive an ecosystem can be. For example, with an abundance of sunlight, water, carbon dioxide, and other minerals, plants could grow exponentially. However, the amount of N in the system creates a threshold for growth. While there are some exceptions (in freshwater ecosystems, the limiting nutrient is usually phosphorus, but that’s a conversation for another day), N is typically the “limiting nutrient” for most of the earth’s Luke Cadrin ecosystems. What’s the problem here, you might ask? Our septic tanks leach wastewater relatively deep into the aquifer, where many of the denitrifying bacteria N is a crucial element that cycles through our do not live, effectively bypassing part of the cycle and ecosystems. Why all the time, effort, and money to sending nitrate-loaded groundwater directly to our get rid of it? forests, ponds, wetlands, and bays. When this happens, the limiting factor for growth is no longer so limiting. Well, humans have globally and locally altered the N cycle. Through industrial production and use of Unencumbered growth of algae and plants occurs, fertilizers, we have increased the amount of “fixed” they compete with one another, then die off and or bioavailable N ten-fold. Since 1970, the global decompose. These effects are drastically changing our population has increased by 78% and reactive N ecosystems: resulting in loss of diversity and resiliency, 1 creation has increased by 120%. The denitrification increasing harmful algal blooms, and more. process does not have the capacity to keep up with the rate we are adding N. This is why the shallow waters and near shore beaches of our estuary are now “muck” instead of sand! Most food we eat on Cape Cod doesn’t originate here or use the locally available N. It was most likely 1 James N. Galloway, Alan R. Townsend, Jan Willem Erisman, farmed using industrial fertilizer containing N and Mateete Bekunda, Zucong Cai, John R. Freney, Luiz A. then shipped here. We consume the excess N, and it Martinelli, Sybil P. Seitzinger, Mark A. Sutton. 16 May 2008. goes straight into our waste. This waste ends up in Transformation of the Nitrogen Cycle: Recent Trends, our septic systems and flows into the groundwater. Questions, and Potential Solutions. Vol 320 SCIENCE. BCleanWater.org Fall/Winter 2025 | Barnstable Clean Water Coalition | 13