Importance of benthic nutrient regeneration during initiation of macroalgal blooms in shallow bays

Eutrophication in coastal areas promotes blooms of green macroalgae that accumulate on the sediment, affecting the exchange of mass and energy at the sediment -water interface. The effects of macroalgal blooms on the microbenthic net metabolism and on the carbon and nitrogen contents of the sediment were studied during an in situ experiment. Two sediment enclosures (with and without macroalgae) of 1.5 × 1. ). This relatively low macroalgal biomass always suppressed the photosynthetic activity of microphytobenthos, decreased the oxygen availability for the sediment and reduced the oxygen penetration depth in the light and in the dark. The microbenthic community metabolism clearly shifted to heterotrophic, while the photoautotrophic activity was located in the macroalgal canopy. This macroalgal mat was net autotrophic, and more productive than the microphytobenthic community inhabiting the bare sediment. Part of the macroalgal production was buried in the sediment, increasing its carbon and nitrogen contents with respect to bare sediment during all seasons except spring. Concentrations of inorganic nutrients in the sediment were always higher below the macroalgal mat than in bare sediment, likely due to a direct input of inorganic nitrogen and phosphate associated with macroalgal debris.

Section: Biomass and Chemical Composition Of Macroalgaementioning

confidence: 99%

Section: And N Contents Of the Sedimentmentioning

confidence: 99%

Section: Accumulation Of Inorganic Nutrients In the Sedimentmentioning

confidence: 99%

See 1 more Smart Citation

Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents

Corzo

Bergeijk²,

García‐Robledo³

2009

“…Most cases of increasing trends in N loads over recent decades have been attributed to elevated NO 3 -inputs to coastal waters (Cloern 2001, Howarth et al 2002, which are largely responsible for increases in the occurrence of macroalgal blooms (Sfriso et al 1992, Valiela et al 1992, Cloern 2001. NH 4 + inputs from raw sewage, aquaculture activities, and dissolved organic nitrogen from benthic nutrient regeneration are increasingly more common, and also support macroalgal production (Trimmer et al 2000, Tyler et al 2001, Sundback et al 2003, Barile 2004, Lapointe et al 2005a,b, Tsai et al 2005.…”

Section: Introductionmentioning

confidence: 99%

Macroalgal responses to experimental nutrient enrichment in shallow coastal waters: growth, internal nutrient pools, and isotopic signatures

Teichberg¹,

Fox²,

Aguila³

et al. 2008

Increased nutrient inputs to temperate coastal waters have led to increased occurrences of macroalgal blooms worldwide. To identify nutrients that are limiting to macroalgae and to determine whether different forms of these nutrients and long-term ambient nutrient conditions affect macroalgal response, we used in situ enrichment methods and tested the response of 2 bloom-forming species of macroalgae, Ulva lactuca and Gracilaria tikvahiae, from shallow estuaries of Waquoit Bay, Massachusetts, USA, that receive different land-derived N inputs. We enriched caged macroalgal fronds with nitrate, ammonium, phosphate, and N + P combinations, and measured growth, nutrient content, and δ 15 N signatures of fronds after 2 wk of incubation. In these estuaries, P did not limit growth, however, the 2 species differed in growth response to N additions. Growth of U. lactuca was greater in Childs River (CR), the estuary with higher nitrate inputs, than in Sage Lot Pond (SLP); growth in SLP increased with nitrate and ammonium enrichment. In contrast, growth of G. tikvahiae was greater in SLP than in CR, but had no growth response to N enrichment in either site. C and N contents differed initially between species and sites, and after nutrient enrichment. Final tissue % N increased and C:N decreased after nitrate and ammonium enrichment. δ 15 N values of the macroalgae demonstrated uptake of the experimental fertilizers, and a higher affinity and faster turnover of internal N pools with ammonium than nitrate enrichment in both species. We suggest that U. lactuca blooms in areas with both high nitrate and ammonium water column concentrations, and is more N-limited in oligotrophic waters where DIN levels are too low to sustain high growth rates. G. tikvahiae has a greater N storage capacity than U. lactuca, which may allow it to grow in less nutrientrich waters.

“…Benthic nutrient fluxes (BNF) can supply a substantial proportion of the nutrient requirements of benthic and pelagic algae in an estuary (30 to 100%) and, thus, they potentially sustain the benthic and pelagic primary production within the estuarine food web (Kemp & Boynton 1992, Berelson et al 1998, Gibbs et al 2002, Sundbäck et al 2003. Generally, investigations of BNF concentrate on the role of microbial processes, associated with coupled nitrification -denitrification, and the microphytobenthos, which intercept the nutrient fluxes at the sediment -water interface (e.g.…”

Section: Introductionmentioning

confidence: 99%

Benthic nutrient fluxes along an estuarine gradient: influence of the pinnid bivalve Atrina zelandica in summer

Gibbs¹,

Funnell²,

Pickmere³

et al. 2005

Benthic nutrient fluxes (BNF) can supply 30 to 100% of the nutrient requirements of benthic and pelagic algae in an estuary, and can, thus, potentially sustain benthic and pelagic primary production within the estuarine food web. While BNF can be influenced by microbial processes, epibenthic suspension-feeding bivalves have the potential to alter fluxes by their influence on the community composition of surrounding macrofauna and benthic boundary conditions, and their feeding activities. In Mahurangi Harbour, New Zealand, the large suspension feeding pinnid Atrina zelandica (hereafter referred to as Atrina) occupies large areas of the harbour floor. Consequently, Atrina have the potential to substantially influence the BNF and, thus, primary production, and the food supply to the filter feeding community within the harbour, including the rack-farmed Pacific oyster aquaculture industry. Mahurangi Harbour is almost always isohaline, but exhibits a strong gradient in suspended sediment concentration, which declines from head to mouth. As Atrina increase their rate of pseudofaeces production with increases in suspended sediment concentration, we conducted in situ light and dark paired benthic chamber experiments with and without Atrina at 4 stations along this turbidity gradient, to determine their effect on BNF. Our results showed substantially greater BNF from Atrina beds than bare sediments. We also found greater net BNF (difference between Atrina beds and bare sediment) in the less turbid water under dark conditions, but enhanced water column nutrient supply in the more turbid water in light, due to Atrina excretion of ammoniacal nitrogen . On an areal basis, we estimate that BNF from Atrina beds may account for up to 80% of the nutrient supply for pelagic primary production and, thus, they are of major importance to the sustainability of aquaculture in this harbour. KEY WORDS: Benthic nutrient flux · Benthic chambers · Estuarine turbidity gradient · Atrina zelandica · Microphytobenthos Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 288: [151][152][153][154][155][156][157][158][159][160][161][162][163][164] 2005 important part of the nutrient dynamics of an estuary (e.g. Newell et al. 2002).Bioturbation and grazing pressure by macrofauna can destabilise the sediments (de Deckere et al. 2001), stimulating microbial activity and enhancing denitrification (Gilbert et al. 1998). However, the presence of large benthic animals may also stabilise the sediments, and affect the composition and functioning of macrofaunal communities (Cummings et al. 1998, Ellis et al. 2000, Norkko et al. 2001, Reise 2002. Abundant suspension-feeders may build loose hummocks, multi-species epibenthic thickets or solid reefs, accommodating diverse epibenthic assemblages. Their raised and rough surfaces alter benthic boundary conditions (Green et al. 1998) and, hence, turbulence (Reise 2002), while their biodeposits may enrich the sediments and smother the microphytobenthos. Bel...