Water Column Turbidity Not Sediment Nutrient Enrichment Moderates Microphytobenthic Primary Production

Abstract

Soft sediment intertidal habitats are under intense anthropogenic pressure resulting from increased land derived sediment and nutrient delivery. Long term, this can cause high water column turbidity and nutrient enrichment of sediment porewaters, which has cascading effects on coastal ecosystem functionality. However, how these stressors may interact and influence benthic productivity over alternating periods of submergence and emergence is largely unknown. This study investigates the effects of sediment nutrient enrichment (at three levels for 20 months) on benthic primary production at six sites in four New Zealand estuaries that spanned a gradient in water column turbidity. While nutrient enrichment had no detectable effect on microphytobenthic primary production, water column turbidity had a significant influence, explaining up to 40% of variability during tidal submergence, followed by temperature and sediment characteristics. In addition, negative net primary production (NPP) estimates and therefore net heterotrophy for the most turbid estuaries during tidal submergence resulted in an increased reliance on production during emerged periods, where NPP was positive across all sites. This study highlights the prominent role of water column turbidity over nutrient enrichment in moderating microphytobenthic production, and the increasing importance of emerged periods to maintain the health and functioning of coastal habitats.

Ecological network analysis of traits reveals variable response capacity to stress

“…The experiment was left for seven months before sampling to allow the nutrients to diffuse through sediments and the ecosystem to respond to the enrichment [ 25 , 27 , 29 ]. During this time an Odyssey PAR logger deployed 10 cm off the seabed at each site recorded (at 10 min intervals) photosynthetically active radiation (PAR) reaching the seabed (giving an ecologically relevant proxy for water column turbidity) [ 30 ].…”

Temporal and spatial variations in benthic nitrogen cycling in a temperate macro-tidal coastal ecosystem: Observation and modeling

“…The absence of a significant difference between benthic flux measurement values under light and dark conditions in our experiment suggests that microphytobenthos had a minor contribution to the benthic fluxes. The high water column turbidity in the VB (Tessier et al, 2011), which limits microphytobenthos development (Mangan et al, 2020), may explain this hypothesis.…”

Drivers for primary producers’ dynamics: New insights on annual benthos pelagos monitoring in anthropised freshwater marshes (Charente-Maritime, France)

“…PB usually dominate shallow lakes and nutrient poor estuaries, because of a better access to light (Drylie et al, 2018;Mangan et al, 2020) and the direct contact with the sediment which is an important nutrient pool (Sand Jensen and Borum, 1990). Concentrations between 9 and 16 µg Chla g sed -1 can be found in temperate intertidal bay estuaries (Orvain et al, 2012), and contributions to more than 1/3 of total primary production in some saline environments (Lake et al, 2011).…”