Seasonal and Interannual Trends in Nitrogen and Brown Tide in Maryland's Coastal Bays

Abstract

Abstract. A retrospective analysis revealed that water quality in the coastal bays of Maryland (USA) has been declining over the past decade, as evidenced by increases in total nitrogenous nutrients and in outbreaks of brown tides caused by the pelagophyte Aureococcus anophagefferns. However, the increases in total nitrogen are not a function of increases in inorganic nitrogen, but rather a function of increases in dissolved organic nitrogen (DON). A near-decadal record (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) demonstrates that an approximate doubling of DON over this time period correlates with a similar increase in total chlorophyll and an even larger increase in the proportion of chlorophyll that is composed of brown tide. Additionally, on an annual basis overall chlorophyll levels and strength of the brown-tide blooms were related to the DON availability that developed during the prior months. Aureococcus anophagefferens is a harmful algal bloom species that preferentially uses DON for its nutrition over inorganic nitrogen forms and thus is a symptom of organic rather than inorganic nitrogen-based eutrophication. These results demonstrate that long-term changes in nutrient quantity and composition have occurred in the coastal bays of Maryland during the past decade and that total phytoplankton biomass, as well as the proliferation of brown tide, are related to these changes. Whether these changes are evidence of a long-term trajectory or represent a shortterm anomaly will be revealed in future monitoring.

Effects of nutrient enrichment in the nation's estuaries: A decade of change

“…There was a 13% increase in the number of systems with 'moderate' to 'high' impact of HABs and a 14% increase in the number of systems with chlorophyll a at 'moderate' to 'high' levels during the past decade, concurrent with increases in nutrient loads (e.g. Kemp et al, 2005;Glibert et al, 2007). In particular, the interest here is in problem occurrences of chlorophyll a and HABs in the mid-Atlantic region lagoons, systems with long residence times.…”

Classifying Ecological Quality and Integrity of Estuaries

“…Excessive amounts of nutrients may, under the right conditions, cause overgrowth of phytoplankton leading to low dissolved oxygen conditions as the bloom dies and the bio mass decays, as well as reduced water transparency which may lead to losses of seagrasses ( Figure 1). Additionally, nutrient additions may cause changes in natural nutrient ratios and/or speciation leading to blooms of opportunistic species, many of which are harmful or toxic (e.g., Aureococcus anophagefferens: Glibert et al, 2007). Because of their direct link and sensitivity to nutrient loading, phytoplankton growth is considered a direct effect (e.g., OSPAR, 2002; WFD methods) or a primary Figure 1 Progression of eutrophication and impact evaluation starting with increased primary production reflected as increased phytoplankton biomass (Chl a) and macroalgal abundance, leading to low dissolved oxygen, losses of seagrasses, and changes in community composition to include nuisance and toxic blooms.…”

Oyster and Macroalgae Bioindicators Detect Elevated δ15N in Maryland’s Coastal Bays

“…Total nutrients, rather than inorganic species, were analyzed according to standard methods (D'Elia et al 1977;Kerouel and Aminot 1987). Long-term nitrogen increases and recycling in these bays have been driven by the dominant dissolved organic fraction (Glibert et al 2001;Glibert et al 2007) and locally are at least moderately bioavailable (Seitzinger and Sanders 1999;Seitzinger et al 2002;Mulholland et al 2004;Glibert et al 2006;Wiegner et al 2006). In culture, Gracilaria cornea efficiently grows on organic (urea) or inorganic (NH 4 + , NO 3 − , or NO 3 NH 4 ) nitrogen (Navarro-Angulo and Robledo 1999).…”

“…Long-term water quality monitoring reported recent degradation and increases in total nitrogen despite historical improvements and decreases in total nitrogen, signaling a need to better understand the driving forces for trend shifts in this region and identify sources of anthropogenic nitrogen ). Symptoms of degradation include an approximate doubling of dissolved organic nitrogen, increasing frequency of harmful algal blooms, e.g., brown tide (Glibert et al 2007), and adverse effects on seagrass distribution and density (Harris et al 2005;Wazniak et al 2007). Human population in Maryland's coastal bays watersheds doubled between 1980 and 2000 to~35,000 people and is expected to double again by 2020 (Hager 1996).…”