In this blog post we will try and consider one of the busiest trading seas in the world, the Danish waters. The Danish seas is considered one of the main trading routes and simultaneously a strategic entrance to the large Baltic sea are which provides crucial access for trading within the Baltic countries, Sweden, Finland and even Russia.
Generally considered a shallow water area, where water depths are above 50 m’s, except for the incredible and unusually deep trench called Skagerrak across the southern tip of Norway.
- Original state of the ocean
- Evolution of nutrient loading towards inner Danish waters.
- The water quality across Denmark
- Marine traffic pressures
- Hypoxia events in Inner Danish waters
- References
In recent years focus have been shifted to try and combat the increasingly frequent occurrences of algae blooms happening in inner Danish waters with a broad variety of consequences for the marine and sea life. These are dependent on the integrate relationships between oxygen, temperature and salinity which is uniquely present for the inner Danish waters and Baltic sea, while also utilizing the broad variety across the year to migrate and multiply within the waters.
The warming of the Baltic seas and change in mixture depth of the temperature-saline halocline challenges the living grounds of particularly the cod, which is an indicator species for the general habitat change present in the oceans. This particular species is particularly interesting as their offspring, eggs, are placed in the halocline floating between the interface between cold saline and warmer waters and thus changes in the depth and placement will have massive consequences for the population. Since the cod is a important food source and a delicacy in Denmark, it is quite important to understand how to support a sustainable fishery industry in these changing environments where temperatures are changing.
Original state of the ocean
Originally Denmark was flourishing with wildlife and animals from dense forests and sprawling seas with a wide variety of species and water quality which were significantly better in the previous centuries before the introduction of fertilizers and industrialized farming practices, but more on that later.
Previously the occurrence of fish within the meat markets is believed to be a primary driver for population growth as people were reliant on catches of fish for food in a higher degree than the introduction of modern day farming practices. The validation of this hypothesis is found through isotope analysis conducted in the differences between the individual cases of the.
This farming practice includes fertilizing the soils and plants leading to increased growth and output of the land areas leading to reduced risks of famine and improved chances of survival for the general population.
Evolution of nutrient loading towards inner Danish waters.
The industrialization of the general public farming practice made it possible for a larger majority of the population to indulge in other activities such as art, culture and service professions. This improved the living conditions for the general public and allowed them to focus on other professions which could help benefit other people increasing their life standards further and causing an increase in living and well-being of the general public.
Related read: Understanding the Significance of the Humboldt Current, Impact of Ocean Currents on Marine Ecosystems.
This provided a substantial change in life-standard for broad parts of society benefiting the human life behavior across all scales. This industrial revolution is one of the main drivers for the benefit of all parts of society from high ranking officials and low born social workers, causing a creation of broader sustenance for all parts of society. However as it turns out the introduction of fertilizers to broader society leads to the generation and contribution of nutrient loading in the resulting environment.
This increased nutrient loading contributes to the general blooming of algae and phytoplankton which when decomposing throughout the water column leads to changes of hypoxia meaning that the increased occurrences of fish-death observed throughout recent years, up towards the decade, is largely influenced by individual farmers filling up their fields with nitrogen rich fertilizers.
The water quality across Denmark
These problematic instances where farmers are interested in increasing yields while simultaneously risks polluting the overall sea around and across the Danish inner seas is a difficult nut to crack and no easy solutions exists since the food security and overall health of the general population is the most purposeful goal of the general population.
Since the industrial age where individual farmers all of a sudden was able to increase yields through use of machinery lead to the discovery of synthetic fertilizers which allowed for increasing yields much further leading to a general food security for developed nations and further adoption of animal stock for eating. This in-turns means that the nitrogen load on the offshore, nearshore and river\lake environments has been increasing with only the recent history
As the nitrogen loads towards the environment leads to increased growth of organic matter in the water column resulting in the amount of oxygen being used for degrading the subsequent organic material. The end result is further eutrophication with asphyxiation events happening more frequently, sadly this means that juvenile and small fish are not given the time to effectively grow big and reproduce meaning that the livestock catch of fish leads to smaller catches and in worst case scenarios population collapse.
Fear of population collapse
The possibility of population collapse is one of the main fears which individual fishermen and industry professionals are faced with. How to effectively increase yields without the use of fertilizers through use of smart farming techniques or changing public perception on food habits is some of the ways which engineers, scientists and farmers are doing in an attempt to combat these changing environments and consequences of industrial farming techniques.
Related reads: Debunking Earth’s Shape: Sphere vs Flat Earth, Environmental impact of offshore infrastructure
As an example of the recent developments within the fishery industries as a result of increased nitrogen loading in the water environments is the fish cod. Cod is one of the most loved fish for human consumption in Denmark and is especially caught during and close to, new years as a delicate meal during the new years eve. This means that the catch rates and size distribution of the cod have been studied in great detail and such data exists following the evolution of cod, see Baltic cod – FishSec, for more information.
The development in catch size of the cod is thus a direct showcase of how the nitrogen loading in the environment is affecting population sizes. However a direct quantification of the interconnected effects are difficult if not impossible to accurately create. Thus the changes in the developments of the individual species and their co-dependent interaction is mainly driven by qualitative descriptions and observations.
Biologists are quite concerned about this development as the ecosystem dynamics effectively change as the nitrogen loading varies, this means that individual small communities of bottom feeding animals low in the food chain is affected by changes in the compositions of the surrounding ecosystem. These changes in food chain compositions directly influences human living as the smaller catch sizes and ranges create pressures on the human eating habits which fish is a big contributor towards.
Innovations towards a cleaner environment
New innovations within farming practices and waste water treatments are underway leading a way towards a smaller sustainable pressure on our water environment in particular in Danish inner seas. Some of the technologies utilized for increasing the purity of wastewater while reducing the loading of pollutants in the environment include among others, nano-bubble technology.
Nano-bubble technology for wastewater treatment
The new innovations within waste water involve the incorporation of a fourth clearing step towards lowering the concentrations of phosphorous and nitrogen in the environment, possible solutions for the developments of new reduction methodologies include among others nano-bubbles where tiny (on the nano-scale) bubbles are utilized to reduce the amount of nitrogen and subsequent loading when released to the surrounding environment.
The scientific processes behind are quite advanced and not suitable for this type of blogpost however the interested reader is more than encouraged to read up on the processes following resources online or at the library, in short, nano-bubbles are superior to regular technologies due to their longer retention times, allowing them to remain suspended within the water column for extended periods of time increasing the efficiency of biological degradation processes involved in the treatment of wastewater.
The nano-bubbles unique emergent features due to their size distributions, high internal pressures, gas transfer rates and the overall interactions with chemical and physical scenarios. This makes it efficient at increasing output purity the of processed water leading to smaller levels of pollutant loading in the environment. With this said it should also be mentioned that the cleaning process requires multiple steps before reaching a sufficient purity of the water for discharging in the environment, which include coarse filtering of fats, oils and insolvable material in sand filters and coarser membranes before being diverted in aeration champers.
Ultra-fine membrane filtering of salts and ions
For the most refined methods a further processing step with reverse osmosis filters can be utilized allowing for the improvement and subsequent realization into a state where salts and ions can be filtered from the water solution turning even salt water into a drinkable solution. This type of filtering is one of the main ways that people in Saudi Arabia and at sea provide drinking water as the fresh water availability in those areas are limited by geographic and natural environments.
Within the Danish seas and waste water treatments, this level of reductions are not utilized as the level of cleanliness does not require such extensive cleaning to be discharged into the ambient sea waters surrounding the Danish seas. Another disadvantage is that the extra saline and ionized water left over after filtration will need to be deposited and handled in a different manner, either through large evaporation pools or designated locations where increased pressures are allowed. These types of contamination areas are not found within Danish territories. However not only the waste water treatment plants are pressuring inner Danish waters, also fishing and shipping industries are pressuring the water quality and overall ecological status of the inner Danish waters.
Marine traffic pressures
Some of the most important pressures in the marine environment in Denmark is the marine traffics which both disturb larger mammals and fish, and discharge other pollutants while also posing a threat of over fishing individuals which are not sufficiently grown into maturity such that individual species cannot reproduce before maturity.
As a way of illustrating the amount of fishing going on in Denmark, annual averages based on AIS data are available for the general public through the EMODnet feature allowing individuals with the information in relation to vessel densities of fisheries.
From the intensity picture we can see that especially the northern part of the Jutland near Skagerrak and Oresund are places where large amounts of fishing is taking place. Furthermore, it is also evident that near Hvide Sande on the western coast of Jutland, a large amount of fishing is taking place, leading to instances where fish populations are under pressure.
Related reads: Impact of Ocean Currents on Marine Ecosystems, Understanding the Significance of the Humboldt Current
The intensities on this figure are yearly averages meaning that this distribution of fish vessels occur over the year, with varying intensity depending on the season of the year and the amount of fish abundant across the Danish inner seas. The exact details of the inner Danish seas and their fish catching quotas is something which is highly debatable across the Danish society.
Furthermore, one of the main adversaries towards sustainable fishing practices is the utilization bottom trawling equipment on large scale. The bottom trawling equipment is a way of fishing where nets are drawn across the seafloor bottom stirring up sediment and leading to increased areas of pressure for ecosystems especially those surrounded with stones and stone reefs. Such instances are highly susceptible towards bottom trawling equipment and the bi-catch rates are significantly larger than other more sustainable fishing practices.
Hypoxia events in Inner Danish waters
Hypoxia events occur when oxygen gets depleted throughout the water column and is typically caused by organisms decaying and thus using up all the available water in the water column. These types of occurrences are becoming increasingly frequent in recent years as the individual The hypoxia events typically unfolding in inner Danish waters is a result of the increased nitrogen loading causing rapidly growing organic material such as algae blooms which later on when decaying cause hypoxia events within the inner Danish waters.
These types of hypoxia events in Danish waters are becoming increasingly frequent following the increased nitrogen loading and the increased fishery intensity especially if these are performed using bottom trawling equipment as such equipment’s stir up sediment with different types of ions located and thus subsequently used up during the organic decay and chemical reactions spurred by the environment. This means that individual instances of hypoxia is sustained for longer periods of time.
References
Lewis, J.P., Ryves, D.B., Rasmussen, P. et al. Marine resource abundance drove pre-agricultural population increase in Stone Age Scandinavia. Nat Commun 11, 2006 (2020). https://doi.org/10.1038/s41467-020-15621-1
The Skjærup blueprint 
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