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2022 > 07

Friday was the second big sampling day for the SITES AquaNet and Aquacosm mesocosm experiment. The experiment is examining the impact of changes in run-off on lake plankton communities since rainfall patterns, and thereby run-off, are expected to be impacted by climate change. Becuase of the diversity of size within planktonic communities and the wide range of factors that can impact both zoo- and phytoplankton, there are a wide range of samples being taken throughout the experiment including; DOC, dissolved nutrients, chlorophyll, phytoplankton, zooplankton, and greenhouse gasses.

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You can’t always see what is being filtered out of water samples with your naked eye, but Lake Erken has a genus of cyanobacteria called Gloeotrichia which forms large colonies that can be easily spotted. These colonies are only one of the many species found in the mesocosms, but during summer they do make up a large part of the biomass.  

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Nutrient and DOC additions follow sampling. Shown below, Stella Berger mixes one of the mesocosms while Silke Langenheder adds nutrients and Jens Nejstgaard tries not to get blown away. Luckily the AquaNet platform is shielded by the dock so it remains relatively stable even in stormy weather. 

Photo by: Matilda Andersson

We look forward to sharing the results of the study in the future!

Surprisingly the extreme snowfall events in early April have not delayed the start of the summer season in the Tarfala valley. A warm May and June caused rapid snow melt and the summer conditions are now quite normal. The discharge in the rivers has been generally high over the last month but has now settled to a normal rate. The ice covering the lake Tarfalasjön is still solid but is expected to break up soon. The Tarfala Research Station opened on June 28th and the SITES sampling program is just now getting started for the year. The station will be run as usual this year after two years of reduced activities.

Tarfala Research Station on April 8, 2022. Photo: Per Holmlund
Tarfala Research Station on July 2, 2022. Photo: Per Holmlund

The wild boar (Sus scrofa) project at Grimsö Wildlife Research Station explores several research topics, including, the effects of supplemental feeding on local boar populations and the surrounding habitat. Supplementary feeding is a management practice where attractive food and nutrients are supplied on daily basis at feeding stations. These feeders are often used in hunting to attract animals to a set location but are also used with the goal of shifting habitat use away from agricultural fields. This project explores whether feeders are an effective way to change wild boar movement within the landscape, protecting agricultural or other sensitive areas but also whether the extra feed over time induces changes in the field layer and plant composition around the stations.

Wild boar inside a baited corral. When the trap is set, the camera screen is monitored and the shutter can be triggered from a distance when a suitable situation is shown.

An effective method to study these questions is to use marked animals. The project uses five different study areas in southern Sweden and has collected movement data from >60 GPS-collared and >300 ear-tagged wild boar. The fieldwork is partly done in collaboration with the landowners, an approach where both parties learn from each other.
 
GPS-collars and ear tags are fitted on adult animals, but during spring the main focus is on piglets. These animals cannot be equipped with heavy collars, due both to their small size and their fast growth but the advantage of tagging piglets is that, once successfully caught, they can be handled without immobilization. Animals with only ear tags do not contribute as much or as detailed information as animals with a GPS, but the marking procedure is comparatively simple and less costly.

Wild boar piglets caught by a camera trap. A feeding station and a trapping coral are show in the back.

The Swedish wild boar population has shown a remarkable increase in the last 15 years and population management is a frequent topic of debate among various stakeholders. Typical issues within the larger debate are; how to reduce boar damage to agriculture and how to evaluate their total cost, as well questions regarding the long-term effects of supplementary feeding of wildlife. These questions are complex and include aspects that may be difficult to study in general and also often vary between regions.
 
Several studies have been published on related topics in recent years, including numerous reports by stakeholder organizations, but many aspects are still unclear. Further knowledge obtained in projects like this is thus awaited and needed by authorities, managers, and land owners.

PhenoCams are cameras designed specifically for tracking the timing of when plants grow buds, leaf out, flower, fruit and die back, the science known as plant phenology. In Abisko, SITES is operating a PhenoCam which is programmed to take pictures towards Mount Nuolja several times per day. The concept of repeat photography has been increasingly used to continuously monitor the foliage and canopy changes mainly because of its low cost, high temporal resolution, high-quality imagery, and automatic operation. SITES Spectral has these cameras set up at 8 different locations across Sweden taking pictures of different plants in an ecosystem. 
PhenoCams record the amount of green (G), red (R), and blue (B) being reflected from those plants throughout the season and the seasonal trends of this color information (digital numbers; DN). Using digital repeat photography scientists can track the seasonal changes in plant development stages. For example, as plants turn green in the spring, the amount of brightness of green in the image increases, and when the plant turns red in the fall, the camera will record that too. The relative image brightness for the green channel over the overall image brightness (i.e., a total of RGB DN) is called the Green Chromatic Coordinate (GCC) while the same with the red channel is defined as the Red Chromatic Coordinate (RCC). These two indices have been extensively used to extract information about phenology. Plotting the time series of GCC or RCC over the years can indicate when the trees begin to turn green, when they are at their greenest, when the leaves begin to turn red, when they are the reddest, and when the leaves start to fall or the trees die back for the winter. The continuous recording of such data over time makes it possible to compare the dates of plants turning green in the spring and dying back and losing their leaves in the fall, to see if the dates change significantly from year to year. To demonstrate this, the images collected between 2015-2020 using the PhenoCam located at Abisko Scientific Research Station (68°21'16" N, 18°48'57" E) were used. A region of interest, which represents the subalpine birch forest, was defined (yellow polygon, Figure 1) to extract the change and plot the change in redness over the study period.

Figure 1. Sample images from PhenoCam located at Abisko Scientific Research Station with Mount Nuolja in the background. A single region of interest (yellow polygon) was used for extracting the time series of RCC.

The daily change in RCC values throughout the study period is shown in the plot below (Figure 2). The date when the smoothed RCC reached the maximum in spring is defined as the Start of Season, and the maximum of the RCC curve in fall (dash-dot vertical line) is the end of the season (EOS) respectively. Only EOS is marked in the plots as the focus here is to extract and compare when the leaves on the trees are the reddest and if there are any changes in the EOS date throughout the study period.

Figure 2. Daily averaged red chromatic coordinate (RCC) from the PhenoCam located at Abisko Scientific Research Station, are shown as hollow gray circles. The hollow circles (black) are the dates of snow within the region of interest. The end-of-season (EOS) dates for each year are shown as dotted lines (black).
The date each year when RCC peaked:
 
Year   Date (mm-dd) Max RCC value
2015   09-15 0.461
2016   09-13 0.449
2017   09-19 0.417
2018   09-10 0.433
2019   09-16 0.451
2020   09-19 0.461

The EOS date across the study period varied between 1 - 6 days in general, except for the year 2018 when the trees turned red a few days earlier than normal. The timing of various plant life cycle events such as the EOS helps us understand how external factors like day length, temperature, and precipitation impact vegetation. We foresee more interesting results as the time series from SITES Spectral grow each year.

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