Online Data

This is a listing of the available online data for the Castle Lake Long-Term Monitoring station. We will be adding to this list over time.

Primary Production

One of the most important biological variables monitored in limnological studies is the rate of photosynthetic carbon fixation, known as primary productivity (PPr). The total amount of PPr in a given aquatic system, as well as the ratio of PPr contributions from planktonic algae, aqatic macrophytes (large aquatic plants), and peryphyton (bottom dwelling algae living on rocks and sediment) is interwoven with a whole series of other variables commonly studied by limnologists. During photosynthesis, CO₂ is combined with water and light energy from the sun to form the sugars the photosynthetic organism depends upon and releases oxygen as a byproduct:

6 CO₂ + 12 H₂O (+ sunlight) --> C₆H₁₂O₆ + 6 O₂ + 6 H₂O

As such, light penetration, and amount of Dissolved inorganic carbon (DIC) from CO₂ all directly affect the reaction. Water temperature is also important as temperature affects reaction speed. As phytoplankton and plants often require other nutrients to survive, levels of chemicals such as Ammonium and Nitrate can also impact the amount of photosynthesis occurring.

Primary Production setup Rate and source of PPr are also closely tied to the structure of the food webs in aquatic systems. Since one of the products of photosynthesis is oxygen, all organisms depending on oxygen for respiration are affected by the amount photosynthesis occurring around them. Oxygen producing planktonic algae and aquatic plants also serve as the food source for many other organisms and the rate at which they are consumed can affect the rate of PPr as well. For example, If the amount of zooplankton increases, their rate of oxygen uptake may increase as may the rate at which they consume phytoplankton. So an increase in the zooplankton community might result in a decrease in PPr. In this way, PPr and resulting amount of oxygen is tied to the food web and may vary as the food web varies in different parts of an aquatic ecosystem.

There are several ways of measuring the rate of PPr commonly used among Limnologists. At Castle Lake, PPr is measured using the ¹⁴C method. This technique employs a carbon tracer that gets taken up during photosynthesis along with Carbon available from CO₂. Water samples are taken at depths spanning the water column. For each depth there is a dark bottle sample and a light bottle sample (one in which photosynthesis can occur and one in which it cannot). Samples are incubated for a fixed amount of time at the depth they were collected, so that light amount and temperature remains constant for that depth. After incubation, the samples are taken to the laboratory and run through a very fine filter. The rate of photosynthesis at a particular depth can be determined by comparing the amount of tracer on the filter from the light bottle with that of the filter from the dark bottle.

Chlorophyll

Chlorophyll is the pigment that algal and plant cells use to absorb solar energy in the form of sugars. This process known as photosynthesis, involves chlorophyll, sunlight, water, and CO₂. In lakes most of the chlorophyll is associated with phytoplankton and periphyton. Since chlorophyll is mostly found algae, this method gives a way to estimate total algal biomass in the lake and its distribution.

We measure chlorophyll at Castle Lake by taking samples from different depths. After zooplankton are filtered out, the samples are filtered again so that all the algal cells (which contain chlorophyll) are collected on a paper filter. The amount of chlorophyll in each sample is measured from their respective filters, giving an accurate estimate of how much chlorophyll there is at each depth. Depending upon the year and climate, chlorophyll concentrations (algal biomass) varies dramatically at different depths. Generally, the concentration changes as the seasons change.

Dissolved Inorganic Carbon (DIC)

The DIC measurement is used to determine the original ¹²C concentration so the Primary Productivity Rate (PPr) can be calculated. In order to calculate primary productivity, the researcher needs to know both how much ¹⁴C was added and how much ¹²C is available to the algae. A water sample for each depth is injected into a vacuum test tube of known volume. A small amount of acid is then injected to convert all inorganic carbon into carbon dioxide. Back in the laboratory at UCDavis, carbon dioxide concentration is measured with an infrared detector. The absorbtion of infrared light is proportional to the amount of carbon dioxide present.

There are many possible carbon contaminants, including air, skin, and many other substances in the lab, so one must be careful while doing this analysis.

GIS Data

Castle Lake Bathymetry

This is a GIS Layer (Shapefile) of Castle Lake's Bathymetry (depth).

Thanks to Brian Welde of Angling Technologies (http://www.findyourwater.com) who digitized the Bathymetry map for us, based off our static image.

Coordinate System: GCS North America 1983
Datum: NAD 83
Projection: California Teale Albers

• Download Shapefile

Invertebrate Collection and Fatty Acid Analysis

Over the history of Castle lake research, several studies have focused on different aspects of the benthos (The benthos encompasses the plant and animal life on and in the bottom rocks and sediments). Recently, however, the Castle Lake Long Term Research initiative has added regular sampling of large insect larvae or benthic macroinvertebrates in an effort to gain a better understanding of where they fit into the food chain and the role that they play in foraging patterns of fish.

Light and Temperature

Secchi Depth

The secchi disk is a white plastic disk that is used to measure the water clarity. The disk is slowly lowered by a marked rope until it is no longer visible, and the depth is noted. Then it is slowly raised until it is visible again. The secchi depth is the average of the two observations.

Secchi disks are widely used because they are durable, transportable, require no power, and--when used consistently--provide a useful measurement of water clarity. The secchi was first used extensively by the Italian astronomer and Jesuit Priest Peitro Angelo Secchi in 1865. It has been used since to measure the transparency of lakes and oceans around the world.

Castle Lake's Secchi depth varies seasonally and inter-annually with an average of 10 M. The world's record Secchi depth is 80 M, observed off Antarctica in October 1986.

Pyroheliometer

The pyroheliometer measures the amount of solar radiation illuminating the earth or, Castle Lake. It is set up next to the lake and the measurements are used in conjunction with other data to calculate the rate and amount of photosynthesis. It also provides a measure of solar heating experienced by the lake, useful in understanding the hydrodynamics of the lake.

It is a relatively simple instrument that records the changes in light
through the expansion and contraction of absorbing black and reflecting silver
metal bands. The expansion and contraction drive a pen on a recording drum.

Nutrient Analysis

All the Castle Lake nutrient analyses involve mixing water samples with various chemicals. These chemicals react with the nutrients, forming a colored solution. The nutrient concentration is proportional to the intensity of the solution's color. A spectrophotometer is used to measure the concentration of the colored compound by measuring the light that it absorbs.

At Castle Lake, we conduct the analysis for Nitrate (NO₃), Soluable Reactive Phosphorus (SRP), and Ammonia (NH₄). Our lab back at UCDavis perform the analyses for Total Phosphorus (TP), and Disolved Inorganic Carbon (DIC).

Thermister Chains

While Castle Lake has been collecting temperature data for a very long time, more recently it has started to collect water temperature continuously at various depths, providing a temperature profile for the lake. A chain, with loggers as various points, is suspended in the lake, and every five minutes (fifteen minutes during the winter months) a value is collected and stored in the logger.

The movie below, created by Dr. Ted Swift, shows the change in temperature over time at various depths up to 14 meters.

On July 23, 2003, a storm blew in over Castle Lake, and the wind changed the temperature profile of the lake dramatically. The storm hits around the 25 second mark!

Water Collection Techniques

Van Dorn

A Van Dorn is a water collection device that is used to collect samples for primary production, water chemistry, and ciliate and rotifer analysis. Plugs are pulled against the tube housing by an elastic rubber tube and then held open by loops of metal cable attached to a trigger mechanism. Once triggered, the plugs snap back into place, sealing the tube and capturing the water from that depth. Van Dorns come in various sizes, capturing different volumes. The Van Dorn is used as a primary collection device, immediately to be poured into secondary containers that return to the lab for the various analyses.

Schindler Trap

A Schindler Trap consists of a clear box with hinged top and bottom. Water flows through as it decends and the top and bottom close as it reaches the desired depth and drawn upward. This prevents further water from entering or leaving and retains a sample of known volume.

Schindler Traps are mainly used to sample for zooplankton collection, as the volume enables the researcher to count the number of zooplankton per unit volume. The enclosure is made of clear material to minimize the visual effect of agile species.

Zooplankton

Collection and Analysis

Zooplankton are tiny crustaceans that live in the lake and feed on algae. Some feed on other zooplankton or tiny ciliates and rotifers. Samples are collected weekly, with with samples taken during the day and the night from the following depths: 0, 3, 5, 10, 15, 20, 25, 30, 32, and a pooled mixed layer (PML), formed from equal amounts from 1, 3, and 5 meters.

A Schindler Trap draws a sample of water from a designated depth, then releases the water to capture the zooplankton. When the samples are counted, the various crestatious species are identified and measured through a microscope. Species of zooplankton observed at Castle Lake include Daphnia, Diaptomus, Holopedium, Bosmina, and others.

The data can be used for several purposes, including a clear profile and density distribution of the various species migration patterns. By measuring their respective sizes, one can calculate their relative biomass, an accurate measure of the lakes phytoplankton growth (tropic level below zooplankton), as well as an indicator of the carrying capacity of lakes fish (the tropic level above).

Bacteria Analysis

The Castle Lake Limnology Lab has started a new study on bacteria, which is part of a California wide study focusing on the linkage between pathological agents and increased human activity in high elevation lakes. Since Castle Lake is experiencing increased human use this study would enable a comparison with similar lakes and the impact of humans and animals at Castle Lake.

Bacteria sampling began at Castle Lake at five different sites, with the goal of capturing various habitat and human activity. Samples are put in vacuum test tubes and taken to an incubator (held at 35 degrees C). Incubation allows strains of potentially harmful bacteria to be counted, if present, including Escherichia coli and Salmonella. They are in the family Enterobacteriaceae that spends a majority of their lives as residents of animal hosts.

So far, the search has not found anything abnormal.

This project is made possible by Dr. Robert W. Derlet of the UCDavis Medical Center.