Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades

Abstract

The first special volume of Limnology and Oceanography, published in 1972, focused on whether phosphorus (P) or carbon (C) is the major agent causing eutrophication in aquatic ecosystems. Only slight mention was made that estuaries may behave differently from lakes and that nitrogen (N) may cause eutrophication in estuaries. In the following decade, an understanding of eutrophication in estuaries proceeded in relative isolation from the community of scientists studying lakes. National water quality policy in the United States was directed almost solely toward P control for both lakes and estuaries, and similarly, European nations tended to focus on P control in lakes. Although bioassay data indicated N control of eutrophication in estuaries as early as the 1970s, this body of knowledge was treated with skepticism by many freshwater scientists and water-quality managers, because bioassay data in lakes often did not properly indicate the importance of P relative to C in those ecosystems. Hence, the bioassay data in estuaries had little influence on water-quality management. Over the past two decades, a strong consensus has evolved among the scientific community that N is the primary cause of eutrophication in many coastal ecosystems. The development of this consensus was based in part on data from whole-ecosystem studies and on a growing body of evidence that presented convincing mechanistic reasons why the controls of eutrophication in lakes and coastal marine ecosystems may differ. Even though N is probably the major cause of eutrophication in most coastal systems in the temperate zone, optimal management of coastal eutrophication suggests controlling both N and P, in part because P can limit primary production in some systems. In addition, excess P in estuaries can interact with the availability of N and silica (Si) to adversely affect ecological structure. Reduction of P to upstream freshwater ecosystems can also benefit coastal marine ecosystems through mechanisms such as increased Si fluxes.

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

“…Indeed, excessive nutrient loading and eutrophication are stressing coastal marine environments throughout the world (Levin et al, 2015). The overabundance of nitrogen in particular the (nutrient usually limiting production (Herbert, 1999;Howarth and Marino, 2006)) causes changes in biomass, structure, and functioning of coastal communities and food webs (Abreu et al, 2006;Howarth et al, 2011;Rabalais et al, 2014). Yet, despite being of paramount importance to global environmental wellbeing, nutrient processing in soft sediments is still poorly understood and response to perturbations are rarely tested experimentally in situ.…”

Performance of the Redfield Ratio and a Family of Nutrient Limitation Indicators as Thresholds for Phytoplankton N vs. P Limitation

“…There is an acute need, however, for critically analyzed N vs. P limitation thresholds in indicators that could be applied to monitoring, modeling, and management of coastal ecosystems (Howarth and Marino 2006). Degradation of aquatic systems by eutrophication is a global problem calling for well-planned and efficient management strategies.…”

“…Historically, marine and terrestrial systems have been considered primarily N-limited (Howarth and Marino 2006;Vitousek and Howarth 1991), whereas predominant P limitation has been the paradigm for lakes (Schindler 1977). Coastal systems represent transitional zones between terrestrial, freshwater, and marine nutrient cycles, appearing thus specifically to call for reliable N vs. P limitation indicators.…”

Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

“…In contrast to many freshwater systems, coastal systems may be N-limited as a consequence of eutrophication associated with high P inputs (Howarth and Marino 2006). Substantial denitrification rates have even been found in N-rich downstream riverine systems, whereas no comparable P-removal process occurs (Billen et al 2009;Vermaat et al 2012).…”