Algal Demand Drives Sediment Phosphorus Release in a Shallow Eutrophic Cove

Abstract

Abstract. Algae play an important role in the internal nutrient cycling of shallow lakes and coves. Algae of shallow water bodies have been shown to thrive and even lead to eutrophic conditions despite a lack of measurable quantities of biologically available phosphorus (P) in the water during summer months. To study how sediment P release and algal growth are connected, water and sediment samples were collected in a shallow eutrophic cove on Beaver Lake in northwest Arkansas. Water quality profiles depicting temperature, dissolved oxygen, nutrients, metals, and photic zone chlorophyll-a were collected weekly from 21 May to 10 July 2018 at three points in the cove: one shallow, one at the cove midpoint, and one at the deepest part of the cove. Cove sediment samples were collected at similar points as the water quality samples for equilibrium P concentration (EPCo) analysis, sediment core incubation, and sediment composition. EPCo for the sediments ranged from 0.024 to 0.027 mg L-1. Sediment cores exposed to aerobic conditions typical of shallow areas had P release rates ranging from 1.37 to 2.02 mg m-2 d-1. Concentrations of soluble reactive P (SRP) in the water column from the weekly water quality sampling averaged 0.002 ±0.003 mg L-1, and photic zone SRP concentrations averaged 0.002 ±0.004 mg L-1 for all sampling sites. The chlorophyll-a concentration increased from 10 to 40 µg L-1 during the period from 21 May to 25 June. When SRP << EPCo, conditions favor the release of SRP from sediments to the overlying water. This was confirmed with the aerobic sediment core incubation in which algal demand was controlled using dark conditions and the release rates were >1.37 mg L-1 d-1. Core aerobic release rates and EPCo conditions both confirmed the release of P under aerobic conditions; however, it appears that algal demand sustained low SRP conditions. This created a nutrient cycle in which algae imposed a nutrient gradient favoring P release by keeping SRP conditions below the EPCo. This study indicates that algal growth potential in shallow water bodies is not limited by SRP concentrations measured within the water column. Studies of shallow water bodies with low SRP concentrations and high productivity should look to the sediments as a source of P to fuel algal growth. Finally, these findings suggest that coves play an integral part in algal production and should not be overlooked when determining the overall P budget for a lake or reservoir. Keywords: Aerobic phosphorus release, Equilibrium phosphorus concentration, Sediment core incubation.

Sediment phosphorus release sustains nuisance periphyton growth when nitrogen is not limiting

“…As hypothesized, aerobic P-flux's measured in from sediment cores collected in May were comparable to release rates measured in other lakes throughout the region (<0.01 to 6 mg m -2 d -1 ) (Haggard and Soerens, 2006;Sen et al, 2007;Haggard et al, 2012;Lasater and Haggard, 2017;McCarty, 2020). With the low P concentrations in the water column of Partners Lake, the sediment may be the primary source of P driving nuisance periphyton growth.…”

“…Phosphorus is released from bottom sediments through desorption to maintain an equilibrium concentration (Reddy et al, 1995;Haggard et al, 2007) and through changing redox potential at the sediment-water interface (Mortimer, 1971). Additionally, photoautotrophs in the water column can influence the environmental conditions overlying lake sediments to promote further P release from the sediments (McCarty, 2020). This P from the sediments can contribute to eutrophication for decades, even after external sources have been reduced (Søndergaard et al, 2003(Søndergaard et al, , 2013.…”

Microcystin Shows Thresholds and Hierarchical Structure With Physicochemical Properties at Lake Fayetteville, Arkansas, May Through September 2020

“…Yet, we do not observe concentrations near this supply in the overlying water at Lake Fayetteville at our three near-shore sampling sites throughout the 2020 growing season. It is common in lakes to have SRP concentrations at analytical detection limits (<0.005 mg L -1 ), and this is likely because cyanobacteria and algae take the SRP up as fast as or faster than the sediments can release it into the overlying water (McCarty, 2019;Austin et al, 2020). We think these sediment P sources are fueling the cyanobacterial growth at this lake, and it might be these internal P sources that sustain the HABs.…”

“…Phosphorus (P) from sediments can fuel algal growth and HABs in inland waters, especially when nitrogen (N) is not limiting (Orihel et al, 2015;Austin et al, 2020). Algal P demand can drive sediment P release in eutrophic waters (McCarty, 2019) when dissolved P in the water is less than concentrations in equilibrium with bottom sediments. This internal P source may result in seasonal N limitation of HABs (Ding et al, 2018), particularly when episodic N inputs are reduced during prolonged droughts.…”

Modeling the Effects of Algal Bloom on Dissolved Oxygen in Eutrophic Water Bodies

“…Tese so-called algal blooms can lead to a release of toxins, taste, and odor problems and fnally the depletion of dissolved oxygen in water bodies [4,5]. Eutrophication is characterized by a signifcant growth of algae due to the overabundance of one or more growth factors necessary for photosynthesis, such as sunlight, carbon dioxide, and nutrients (nitrogen and phosphorus) [6,7]. When algae are starting to grow in an unrestrained manner, an increasingly large biomass is formed, which is destined to demote.…”