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The Data: Haarlemmermeerse Bos



By Axel Gunderson

We have been collecting temperature, visibility, and photographs from the man-made lake in Haarlemmermeerse bos, a 115-hectare park-like area to the northwest of Hoofddorp in the Netherlands since November of 2011. Our location is a citizen science playground.

The lake is isolated, fairly small (22 hectares) with a maximum depth of 20 meters. The most interesting feature is a water mixing system, which the water authority phased out over a period of three years. It had been operational since 1999 to help minimize cyanobacteria blooms until 2012. In 2013, the mixing system first became inactive because it was written off due to the expense. In June 2014, we still found five varieties of stonewort (Chara), which represents good water quality and is a perfect visible bioindicator. In August 2014, the first cyanobacteria bloom was suppressed by starting the mixing system again, which was kept in standby mode between 2013 and 2015.

As of 2013, the spined loach, a native fish, disappeared. It had been around for years as well as a species of freshwater jellyfish, but the latter can be related to stratification. The jelly fish reappeared in 2015 when the mixing system was active (at 40% power) for the entire season and no cyanobacteria blooms occurred. Stonewort, an aquatic plant species of the genus Chara and a valuable bioindicator, went from five to one species in two years’ time. As of 2017, stonewort had disappeared from the lake. Funny enough, the two main parameters, vertical visibility and temperature, remained rather constant over the span of seven years. The average temperatures are between 11.7 and 13.6 degrees Celsius at three meters depth, and the average vertical visibility is between 5.5 and 6.1 meters.

These two parameters did not seem to correlate with the disappearance of the stonewort. Chemical values of the water did change rather drastically though. Thanks to Harry van Goor, a rise of phosphate levels since 2014 was measured. That is just one of the catalysts for cyanobacteria blooms. This is a fact: Warm, high-phosphate water (upto 1,8 Mg/L) is pumped in surface water of the lake in the summer to maintain a certain water level. A sufficient water level allegedly prevents the influx of saline well water.

In 2018, hydrogen peroxide was applied to kill cyanobacteria for the first time. Two weeks later, another cyanobacteria species became very abundant. We also noticed a high mortality rate amongst older bivalves (freshwater molluscs), while younger specimens were unaffected.

My view based on collected data is that a new water mixing system suppresses cyanobacteria blooms but can’t stop them, and it’s very expensive. But, what if the phosphate source was taken out of the equation? Our goal for 2019 is to monitor saline levels near the bottom in relation to fluctuating water levels. Our Project Baseline initiative reports changes to the water agency, as well as vets ideas and theories about the status of the lake. Check out the data collected in the lake by visiting the Project Baseline’s online spatial database. View more of our data.

The most worrying is this graph of phosphate levels in 2018. Blue bars represent 2017 and red bars represent 2018. Graph by H. van Goor
Average phosphate levels over 5 years. Graph by H. van Goor
Temperature data recorded in the lake by PB: HBOS from 2011 until 2018. Temperature is displayed in Celsius and taken at a depth of 3 meters.
Visibility data was collected at the same place as the temperature from the graph above. The visibility is recorded using a Secchi disk. The Project Baseline: HMBOS
team monitors this station every two weeks, and changes are sometimes very spectacular. The station is on one of the vertical concrete piles that supports a restaurant and stands free in the water at about 13 meters. At 3 meters depth, a simple station was created by using a rope tied around the pile. At this depth, light and temperature are variable during seasonal changes.

Interested in more data? Check out last month’s data highlight.

Axel Gunderson has been diving for 12 years and can’t get enough of it. In 2011 he got his GUE Fundamentals certificate.That soon lead to starting a Project Baseline location in his favorite lake, which lies in the town of Hoofddorp in the Netherlands.

The Project Baseline initiative is driven by data collection. With an online spatial database that hosts the collection efforts of over 100 teams in over 30 countries, anyone can access the temperature, visibility, and images from these aquatic locations.



Maritime archeologist Matt Carter discusses what brought him to Chuuk Lagoon and his quest to call attention to the oil leaking from WWII shipwrecks, the focus of the Major Projects Foundation, where he serves as Research Director. The foundation was created with the goal of working with Pacific nations to protect their marine ecosystems from potential oil spills from WWII shipwrecks, and is currently working to determine determining how much oil the ships lost in the Asia-Pacific region still hold. Previously a team of international experts calculated the amount of oil to be anywhere between 150 million and 1.2 billion gallons.




Header image by Steve Trewavas. The port propeller of the Rio de Janeiro Maru clearly showing the huge scale of the shipwreck.

Maritime archeologist Matt Carter discusses what brought him to Chuuk Lagoon and his quest to call attention to the oil leaking from WWII shipwrecks, the focus of the  Major Projects Foundation (MPF), where he serves as Research Director. The foundation was created with the goal of working with Pacific nations to protect their marine ecosystems from oil spills from WWII shipwrecks.

What many people know is that between 1939 and 1945, the Japanese military and the Allied powers fought an increasingly bloody war through South-East Asia and out across the Pacific Ocean. What fewer people know is that this maritime war saw the loss of some 3800 ships which sank, taking with them their crew, cargoes, and in some cases huge volumes of toxic heavy fuel oil. 

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A volunteer cleaning oil spilled from the wreck of the MV Wakashio in August 2020. (Photo: Shutterstock)

One of the questions that Carter is asked frequently is how much oil could these ships possibly still be holding today? In 2005, a team of international experts came together to answer just that question. Searching through archives for information on these potentially polluting shipwrecks (PPW), they calculated that combined, all of the ships lost in the Asia-Pacific Region could possibly still hold anywhere between 150 million and 1.2 billion gallons of oil!

MPF was established in 2018. After signing a memorandum of understanding with the Secretariat of the Pacific Regional Environment Programme (SPREP), the foundation began reviewing and prioritizing the 3800 WWII shipwrecks sunk in the Asia-Pacific Region, resulting in a priority list of 55 PPW deemed to be the highest environmental risk. Seventeen of these wrecks are located in the world-famous diving Mecca of Chuuk Lagoon in the Federated States of Micronesia.

One of the key tools that the foundation used for investigating the condition of the PPW in Chuuk was photogrammetry, a process where a wreck is scanned by divers taking thousands of overlapping photos which are then run through a 3D software program. The main focus of this photogrammetry work was the wreck of the Rio de Janiero Maru, as oil leaks from the wreck were thought to have impacted nearby mangroves in 2008. Over multiple dives, the foundation surveyed and scanned the shipwreck taking 7350 photos and three hours of video. This was the first time that any of the wrecks in Chuuk Lagoon had been recorded in this way resulting in the 3D model shown below. 

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3D model of the 140-metre-long Rio de Janeiro Maru. The model comprises 7,350 high-resolution images Photo Dr. Matt Carter/Major Projects Foundation

From this survey, Carter was able to create a baseline condition assessment of the Rio de Janeiro Maru including a hull integrity assessment that has allowed for a more accurate estimation of the amount of oil that may remain inside the wreck. This information was subsequently incorporated into a ‘Likelihood of Oil Release’ assessment providing MPF and the Chuukese authorities with a greater understanding of the potential threat that this wreck poses.

The survey of the Rio de Janeiro Maru has shown what can be achieved through the combination of marine archaeology, technical diving, and photogrammetry. However, this is only the first of the 55 potentially polluting wrecks throughout the Pacific that MPF and its partners urgently need to assess in order to mitigate the impact that these ticking ecological time bombs will have on the people and marine ecosystems of the region. 

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