Warming weather, ‘blooming’ ponds

An example of early climate change in Rappahannock County ponds?

By Michael A. Champ

Special to the Rappahannock News

In January 2017, scientific agencies around the world, including NASA and NOAA in the United States and the MET Office in the United Kingdom, named 2016 the warmest year of record. This is the third consecutive year with a new record temperature. The 2016 record meant that 16 of the 17 warmest years have occurred since 2000.

A pond near Flint Hill covered by spiraling and water shield, a member of the water lilies.

This year, I treated my first pond with a Spirulina algal bloom in February. Normally algal blooms occur in summer and mostly in older ponds. The question is, what is causing these early algal and plant blooms?

In addition to algae, other aquatic plants are also blooming early this year, such as watermeal, Lemna minor, a free-floating plant. Watermeal is the world’s smallest flowering plant and can quickly cover the entire surface of a pond. Watermeal undergoes cell division logarithmically every 4 hours of bright sun.

The easiest way to identify watermeal is to stick your finger in the water and the cells will cling to your finger. When you rub your fingers together, the watermeal will feel gritty.

Another plant blooming early is common duckweed, Wolffia spp. It is also tiny (1/16th to 1/8th inch), light green, seed bearing, with up to three leaves or fronds, with a single root hair from each frond, and is free-floating on the water’s surface.

A major way that duckweed is introduced into ponds is from bird’s feet. Duckweed likes calm waters with low wind, waves or turbulence. It likes to hide in sheltered areas behind cattails or in floating decomposing cattail stalks. If the colonies cover the surface, oxygen is depleted and fish kills occur.

Limnologist and pond experts see algal and plant blooms predominantly in ponds 10 years or older, and/or shallow water ponds (smaller water volume and surface area). In larger ponds, the size and degree of the shallow water zone (4 feet or less with a slope of 1-3 feet) and water turbidity help reduce excessive plant growth. These ponds have undergone eutrophication, the buildup of rapidly cycled organic carbon taking oxygen out of the water due to excess nutrient loading. The source of the nutrient loading may be from horse and cattle runoff, geese feces, agricultural and yard fertilizers andor the annual volume of leaves (which can take 3-years to decompose) from surrounding trees.

Beginning last year, some older, shallow ponds in Northern Virginia, we began to see Spirulina filamentous algal growth in columns (3-4 feet tall and 3+ feet wide) from the bottom to the surface.

Normal treatment strategies with available commercial aquatic herbicides that can be sprayed on the surface of a pond appear to only kill of the floating algae and thus it comes back at the surface quickly.

This year, we had a span of spring-like weather resulting in excessive algal and plant growth in February and March. This is unusual in this area. Recent warmer winters, coupled with periods of cold/freezing weather has produced warmer bottom waters in ponds. As a result Spirulina and other plants grew all winter.

Reflecting on this, we wonder if this is an example of early climate change in ponds in Rappahannock County and Western Virginia.

A similar question is being asked by entomologists as they see the early emergence of the 17-year Brood IX Cicadas in May (14th year), across the Mid-Atlantic region as reported by the Washington Post. Is this also due to warmer recent winters and springs and another example of early climate change?

Michael A. Champ, Ph.D. Limnologist, works with ponds in Rappahannock County. He can be reached at drmikechamp@gmail.com

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