Algae and Dissolved Oxygen Dynamics of Landa Lake and the Upper Spring Run

Transcription

1 Algae and Dissolved Oxygen Dynamics of Landa Lake and the Upper Spring Run

2 Why study algae and dissolved oxygen dynamics of Landa Lake and the Upper Spring Run? During low-flow conditions, extensive algal mats and floating vegetation mats develop in Landa Lake. o Anecdotal evidence suggests that the benthic algal mats have significant negative impacts on aquatic macrophytes and bryophytes through shading. o Loss of macrophytes and bryophytes = loss of fountain darter habitat. It has been postulated that floating vegetation mats negatively affect oxygen dynamics in Landa Lake, through shading and decomposition, which could negatively affect fountain darters. o Is the affect of the floating vegetation mats on dissolved oxygen sufficient to affect fountain darters?

3 Two Components to Study 1. During low-flow, does algal mat formation negatively affect macrophytes and bryophytes? 2. Does the floating vegetation mats affect dissolved oxygen?

4 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13 Jul-13 Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Jul-14 Aug-14 Sep-14 Oct-14 Nov-14 Dec-14 Jan-15 Feb-15 Mar-15 Apr-15 May-15 Jun-15 Jul-15 Aug-15 Sep-15 Oct-15 As much as we like rain, it did not cooperate for this study January 2013 October 2015 Comal River Average Monthly Flow (cfs) 50 Avg. Monthly cfs Provision M (cfs)

5 During low-flow, does algal mat formation negatively affect macrophytes and bryophytes? Despite not having low-flow conditions, there were some valuable findings. Algal mat influence on macrophytes and bryophytes was found to be negatively affected by flow. o High-flow restricts the formation of algal mats. Nutrient studies showed that the system is phosphorus limited. o (N:P ratio = 221; very high) Spirogyra and Cladophora typically make up the algal mats. During the 2015 improved flow conditions, Spirogyra was dominant; however, Cladophora may dominate under different flow conditions. The next time there is an extended drought, it is recommended this study be done to determine the impacts of low-flow.

6 Vegetation biomass for each of the four vegetation types through the experimental growth period. A and B show the no-algae plot where algae was mostly absent if it was observed. C and D show the +Algae treatment. The p-value of a Student t-test comparing the final biomass in the +Algae treatment and the Reference Plot is shown.

7 Does the floating vegetation mats affect dissolved oxygen? In 2015, the vegetation mats did not deplete DO to the point that it was too low for fountain darters. o Relatively little of Landa Lake had vegetation mats and low, overnight DO. o There were some dissolved oxygen problems in isolated, low-flow stagnant areas. DO conceptual model of Landa Lake showed greater influence from atmospheric conditions, water column algae, and macrophyte activity than decomposition of vegetation and vegetation mats. If vegetation mats were to cover 25% of the surface of Landa Lake, that could have a significant effect by reducing surface aeration.

8 Daily maximum and minimum levels of dissolved oxygen at Mat #1. Top Panel shows data for the top of the water column. The bottom panel shows data for the sensor near the sediment surface. Yellow symbols are used for sensors outside the mat. Black symbols for sensors inside the mat. Circle are used for sensors at the top of the water column. Down triangles are used for the near-bottom sensors.

9 Where to go from here Low-flow conditions have the potential to alter algal communities, both by abundance and species. Low-flow conditions may cause more algal mats and floating vegetation mats to form. Due to Mother Nature, the algae mat portion of this study could not be conducted in-situ, under low-flow conditions. This study provided excellent information for normal to high-flow; it should be considered for repeating during a year of low-flow. The results of this study may be useful to the Eco-Model.