A study of species at the Medellin river and their relationship to river pollution

1. 1
Review Article, Expert Opin Environ Biol Vol: 7 Issue: 1
A Review on Study of Macro
invertebrates Specimens in the Medellin
River of Colombia and their Relationship
to Water Quality
Enrique Posada*
HATCH INDISA S.A.S., Engineering Consultancy Group, Medellín, Colombia
*Corresponding Author : Posada Enrique
Engineering Advisor at HATCH INDISA S.A.S., Engineering Consultancy Group,
Medellín, Colombia
Tel: 5744446166
E-mail: enrique.posada@hatchindisa.com
Received: March 10, 2018 Accepted: March 28, 2018 Published: April 02, 2018
Citation: Posada E (2018) A Review on Study of Macro invertebrates Specimens in
the Medellin River of Colombia and their Relationship to Water Quality. Expert Opin
Environ Biol 7:1. doi: 10.4172/2325-9655.1000151
Abstract
The Medellin River is the main body of water in the Aburra Valley in Colombia. It is a
highly polluted river, which is now in the process of being cleaned, under a program
being executed by EPM, the local state-owned utility. The environmental authority in
the Aburra Valley region is the AMVA (AREA METROPOLITANA DEL VALLE DE
ABURRA), which has overseeing power to regulate emissions to the river and to attain
the required water river quality, as demanded by the existing regulations. As the
Aburra Valley is an area where near 4.0 million people live, being also an important
industrial, commercial, financial and educational center, the pollution loads are sizable.
Given that the existing water treatment system is clearly insufficient, the water quality
of the river is poor. AMVA contracted a group of four local universities to develop a
very complete and complex study and set of data, to characterize the river and to
understand its environmental situation in an integral and comprehensive way. This
article uses a previous study of this set of data oriented towards establishing quality
indexes based on temperature and oxygen demand, to establish correlations with
biological information gathered in the AMVA study, in the case of macro invertebrate
specimen data. It is concluded that there is a clear correspondence between the
abundance of individual macro invertebrate specimens and the water quality.
Keywords: Medellin River; Water quality; Valle de Aburra; Macro
invertebrates; Quality index

2. 2
A review of study of macroinvertebrates specimens in the Medellín River of Colombia and
their relationship to water quality
Enrique Posada
Hatch Indisa S.A.S
enrique.posada@hatchindisa.com
Abstract: The Medellín River is the main body of water in the Aburrá Valley in Colombia. It is
a highly polluted river, which is now in the process of being cleaned, under a program being
executed by EPM, the local state-owned utility. The environmental authority in the Aburrá Valley
region is the AMVA (AREA METROPOLITANA DEL VALLE DE ABURRÁ), which has
overseeing power to regulate emissions to the river and to attain the required water river quality,
as demanded by the existing regulations. As the Aburrá Valley is an area where near 4.0 million
people live, being also an important industrial, commercial, financial and educative center, the
pollution loads are sizable. Given that the existing water treatment system is clearly insufficient,
the water quality of the river is poor. AMVA contracted a group of four local universities to
develop a very complete and complex study and set of data, to characterize the river and
understand its environmental situation in an integral and comprehensive way. This article uses a
previous study of this set of data oriented towards stablishing quality indexes based on
temperature and oxygen demand, to stablish correlations with biological information gathered in
the AMVA study, in the case of macroinvertebrate specimen data. It is concluded that there is a
clear correspondence between the abundance of individual macroinvertebrate specimens and the
water quality.
Keywords: Medellín River, Water Quality, Valle de Aburrá, Macroinvertebrates, Quality Index.
1. Introduction
The Medellín River is the main body of water in the Aburrá Valley in Colombia. It is a
highly polluted river, which is now in the process of being cleaned, under a Sanitation
Program being executed by the local state-owned utility, called EMPRESAS PÚBLICAS DE
MEDELLIN (EPM), which also has the responsibility of supplying clean water for
consumption. The total processing capacity for this supply system is currently 10.97 m/s.
EPM is also responsible of controlling water pollution coming from water use. This is being
done in phases. The first one involved the construction of the San Fernando Wastewater
Treatment Plant in the south of the Aburrá Valley, with an investment of US $130 million
and an effective treatment capacity of 1.47 m3/s. The San Fernando Plant has been working
since 2000. At present time, (2018) EPM is building the Bello Wastewater Treatment Plant
as part of the second phase of the Medellin River Sanitation Program. This plant will treat
80% of the wastewater from the Aburrá Valley and 95% of the overall treated wastewater
dumped in the Medellin River. [1]. This complex project, which was originally planned to be
operative in 2015, is still in the final construction details and will be fully operative in 2018-
19. It involves the construction of a huge interceptor, with a length of 7.7 km and a diameter
between 1.8m and 2.4m. [2].
The new wastewater treatment plant will receive around 120t a day of industrial,
commercial, and residential organic waste. The plant will be designed for a treatment

3. 3
capacity of 5.0 m/s, based in an infrastructure for biological treatment by activated sludge
and fine bubble aeration, sludge digestion, and energy recovery, as well as odor control. The
will mean investments around 400 US $ million.
The environmental authority in the Aburrá Valley region is the so called AMVA (AREA
METROPOLITANA DEL VALLE DE ABURRÁ). It has the overseeing power to regulate
emissions to the river and to attain the required water river quality, as demanded by the
existing regulations. As the Aburrá Valley is an area where near 4.0 million people live, being
also an important industrial, commercial, financial and educative hub, the pollution loads are
sizable. Given that existing water treatment system clearly insufficient, the water quality of
the river is poor.
Under that context AMVA contracted a group of four local universities to develop a very
complete and complex study, to characterize the river and understand its environmental
situation in an integral and comprehensive way [3]. This study involved numerous sampling
phases in a set of 20 sampling stations, labeled E1 (near the starting of the river at the San
Miguel mountain) to E20 (a place when the river changes its name to Rio Porce, after the
mouth of the Rio Grande, at the Gabino Bridge station. A monitoring campaign carried in
2006-2007 included measurements of different variables such as dissolved oxygen (OD),
water temperature (T), air temperature in the area (TA), conductivity, nitrogen, metals, and
presence of macroinvertebrates and microorganisms, among others. Table 1 shows the list of
the monitoring stations with their altitudes. In stations E4 and E10 samples were taken in two
of the major streams that flow into the river, a few meters before their mouths to the main
stream.
The author did a previous study of this data oriented towards stablishing quality indexes
based on temperature and oxygen demand [4]. In the present work, these quality indexes are
used to stablish correlations with biological information gathered in the AMVA study, in the
case of macroinvertebrate specimen data.
2. The Medellín River and the sampling of macroinvertebrate specimens
This river forms the Aburrá Valley in the zone of study. It comes down from the San
Miguel mountain at the south of the Valley, as a fast-flowing stream and enters the Valley
proper, at a height of 1860 m above sea level (m.a.sl) in the municipality of Caldas. In the
valley, the river runs for some 100 km, up to the northern limits of the municipality of
Barbosa, at a height of 1100 m.a.sl. The river medium velocity oscillates between 0.50 and
1.30 m/s in the valley according to the site. Figure 1shows the Valley and the Medellín River.
Samples were taken by specialized personnel from the participating universities. It is
reported [3] that for each sampling station a five-minute sampling time was applied. In
general (with exception of the first station, San Miguel, where the river is starting to flow
and is still quite clean and low in flow and where a screen network placed in the in the flowing
area was also used) a D-net network was employed on one of the banks of the river. This [5]
is a dip net nylon 500-micron mesh placed on a 12-inch-wide frame. A shovel and a recipient
was used in the zones of accumulation of sediments for extracting them. The researcher report
that the collected material was stored in plastic bags, previously labeled with the date of
sampling, the name and number of the station and were preserved in 96% alcohol and
subsequently taken to the Alexander von Humboldt Limnology Laboratory in the Institute of

4. 4
Biology of the University of Antioquia, for the separation, identification and counting of
organisms.
Figure 1 The Medellín Valley in its passage through the Aburrá Valley from the San
Miguel station in the south to the Puente Gabino station in the north. Sites of sampling
stations E1 to E20 along the river are indicated. Urban areas are enclosed with red lines
3. Data obtained
Table 1 shows the water quality data obtained in the study, which was based in 10
samples taken in 10 different days between March 2006 and August 2007. The table shows
the main parameters here considered, with their averages and their statistical variations put
in term of the standard deviation for the ten samples, expressed as percentage of the average
value. The parameter that shows the largest variations is the flow. For station E14 (at the site
Parque de las Aguas), no water quality parameters were monitored during the considered
sampling season.

5. 5
Table 1 Main water quality parameters for the 20 station and their variations
Sampling station E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 E12 E13 E15 E16 E17 E18 E19 E20
Site
SanMiguel
Primavera
AncónSur
DoñaMaría
AntesdeSan
Fernando
DespuésdeSan
Fernando
Puente
Guayaquil
AulaAmbiental
PuenteAcevedo
QuebradaLa
García
PuenteMachado
AncónNorte
PuenteGirardota
Hatillo
Papelsa
Popalito
Pradera
EADE
PuenteGabino
Altitude m.a.sl. 1863 1802 1643 1550 1513 1509 1476 1462,5 1449 1440 1431 1412 1368 1350 1319 1270 1192 1146 1098
Flow, m/s 0,8 1,9 4,5 7,3 8,1 9,4 16,6 23,1 29,1 35,9 37,8 44,6 65,9 71,0 74,6 77,2 127,6
SD Flow, % 70,2 57,7 42,8 35,8 33,6 25,3 35,6 47,3 49,9 43,4 45,9 38,3 49,9 49,9 49,9 49,9 49,9
Air temp. °C 18,6 18,5 23,8 23,4 24,9 23,3 26,7 24,2 20,5 20,7 25,1 23,9 27,8 22,6 20,7 24,4 26,3 27,2 25,5
SD Air Tem., % 8,3 5,3 4,8 8,7 9,9 5,2 10,7 4,0 6,2 6,9 7,4 3,7 5,5 7,6 6,7 13,0 8,4 6,8 4,9
Water temp, °C 16,5 16,9 19,5 20,0 21,0 20,7 22,5 21,2 19,3 18,7 21,0 21,6 22,2 20,5 19,0 20,6 21,7 22,2 21,9
SD Water T., % 4,5 3,9 3,2 6,6 5,5 7,1 8,1 5,1 6,6 10,1 3,9 4,3 5,5 3,6 3,3 8,9 6,3 6,9 3,3
pH 6,9 7,1 7,5 7,5 7,5 7,3 7,4 7,5 7,5 7,6 7,6 7,3 7,5 7,2 7,2 7,3 7,5 7,3 7,3
SD pH., % 8,7 6,3 5,3 4,9 6,6 5,7 6,2 0,8 5,6 5,3 5,9 2,9 4,0 1,5 3,6 2,3 3,5 3,8 2,5
Conductivity MS 31,0 54,4 115,6 191,2 156,1 344,3 310,9 259,5 317,7 219,1 349,3 369,8 338,0 271,9 287,3 248,2 263,3 247,6 207,3
SD Cond., % 29,5 16,9 18,0 29,1 23,3 43,5 40,3 34,9 38,9 40,9 27,1 26,4 24,5 30,8 33,1 29,2 28,9 28,6 25,5
DO mg/l 7,31 6,80 5,92 4,51 6,10 5,38 4,13 5,39 3,35 4,27 2,60 2,22 3,44 3,40 6,51 7,29 6,62 5,69
SD DO., % 5,0 6,9 11,1 34,9 2,3 16,7 31,8 17,8 55,9 34,6 71,7 61,7 35,1 40,4 13,7 4,1 14,3 14,9
ICOD 9,33 8,69 7,95 6,17 8,31 7,36 6,00 7,42 4,55 5,50 3,91 3,49 5,07 4,67 8,25 9,45 8,79 7,55
SD ICDO, % 5,4 6,6 11,4 30,9 4,2 12,4 24,0 13,6 50,3 29,6 59,2 44,8 29,3 37,4 14,0 3,8 12,0 14,2
ICT 10,0 9,6 8,4 7,9 7,1 7,1 6,2 6,9 7,7 8,4 7,3 6,4 6,8 7,1 8,1 7,4 6,9 6,6 6,5
SD ICT, % 5,0 8,7 7,6 12,4 11,4 16,9 24,0 14,5 18,2 20,6 13,8 16,9 19,4 9,1 8,7 18,4 17,6 19,7 12,0
Ical DOT 9,53 8,98 8,10 6,68 7,99 7,29 6,19 7,25 5,40 6,36 4,84 4,35 5,58 5,41 8,19 8,88 8,00 7,19
SD Ical DOT, % 3,0 5,0 6,3 20,5 2,1 12,5 21,4 13,4 30,8 23,2 36,7 31,3 20,4 23,1 8,4 4,2 13,1 10,5

6. 6
Figure 2 shows the average behavior of the water parameters and quality indexes for
each sampling station.
Figure 2. Average water and air temperatures, water parameters and water quality
indexes for the sampling stations

7. 7
Figure 3 shows the correlation of the combined Temperatures Dissolved Oxygen water
quality index (Ical DOT) with river flows for all the sampling stations. The variations for
each station correspond to the sampling dates.
Figure 3 Correlation of river flows with combined water quality indexes for each
sampling date
Figure 2 indicates that the river experiment a deterioration in the DO (dissolved oxygen),
an elevation of the temperature and low quality indexes in its pass through the large populated
zones, which correspond to sampling stations E4 to E15. In passing from stations E5 to E6
the river receives the flow coming from the San Fernando treatment plant, experimenting a
recovery in the quality and an increase of flow, but also a large increment in the conductivity,
probably duo to the addition of chemicals in the water treatment that generate soluble salts.
After station E14 the river receives an inflow of cleaner water coming from a Río Grande
diversion which causes larger flows, lower conductivity and better water quality.
Table 2 shows the list of the macroinvertebrates found and identified in the study,
grouped by orders. A simple description is given, for better reading for the non-specialist. In
figure 4, photographs are shown for the same reason for some representative families or
genera. The total average number of individuals in each sample run was 4.300, with an
average per station of 215. The more abundant order was the Diptera, with 55 % of the
individuals. Figure 4 shows the average prevalence of total individuals per station during the
10 sampling campaigns.

8. 8
Table 2 List of orders and prevalent macroinvertebrate families found in the samples and general statistics
Order Description
# of
fami-
lies
found
Prevalent families
% of
specimens
found
Total
average
specimens
all
stations
Average
per
station
Standard
Variation,
%
Tricladita Turbellarians, flatworms. 1 Dugesiidae 0,06 3 0,13 393
Haplotaxida Annelids, ringed or segments worms 1 9,54 410 21 236
Rhynchobdellida Jawless leeches 2 Glossiphoniidae 1,73 75 4 258
Basommatophora Air-breathing slugs and snails 4 Physidae 8,76 377 19 276
Mesogastropoda Freshwater snails 2 0,02 1 0 205
Veneroida Bivalve mollusks 1 Sphaeriidae 0,01 1 0 287
Collembola Springtails. Hexapods no considered insects 1 Isotomidae 0,21 9 0 252
Ephemeroptera
Aquatic insects: mayflies, shadflies or fish
flies 10
Baetidae, Leptohyphidae,
Leptophlebiidae 9,31 400 20 340
Odonata
Carnivorous insects (dragonflies,
damselflies) 10 Calopterygidae, Gomphidae 0,83 36 2 281
Plecoptera Insects known as stoneflies. 1 Perlidae 0,73 31 2 444
Hemiptera “True bugs” insects 7 Naucoridae, Veliidae 1,00 43 2 369
Megaloptera Insects with large and clumsy wings 1 0,03 2 0 417
Coleoptera Beetles 33 Elmidae 3,01 130 6 328
Lepidoptera Butterflies and moths 1 Pyralidae 0,10 4 0 327
Trichoptera
Caddisflies. Insects with aquatic larvae and
terrestrial adults
14
Calamoceratidae, Glossosomatidae,
Hydropsychidae, Helichopsychidae,
Leptoceridae 9,49 408 20 421
Diptera “True” flies. Insect with two wings 40 Chironomidae, Tipulidae 55,15 2372 119 71
Hydracarina Water mites 1 0,02 1 0 447
Decapoda Crustaceans including prawns, shrimp 1 Palaemonidae 0,01 1 0 178
Total 100 4302 215 106
SD between
samples,% 25

9. 9
Figure 4 Images of specimens belonging to the orders of macroinvertebrates found in
the study. Taken from the literature (references shown)
Figure 5 shows the abundance of individual found for each sampling station, indicated
by the average total of individuals for all orders in the ten sampling campaigns,

10. 10
Figure 5 Average total of individuals per sampling station and average numbers for
the more prevalent families
It is seen that sampling station E9 to E14 show the less abundant presence of
macroinvertebrates, while station E1, E2 and E20 show the largest presence. Of course, this
has to do with the quality of the river waters as will be shown. The more abundant genera
was Diptera Chironomidae larva, with larger presence in stations E1, E2 and E 20, which are
also the ones with better water quality. Order Haplotaxida is the one more abundant in lower
quality waters.
4. Correlation between abundance of macroinvertebrates and water quality
Figures 6 to 8 propose some correlations between the total number of individuals and
the water quality.

11. 11
Figure 6 Correlations between total abundance of macroinvertebrate individuals for
all sampling station during the different campaign days and their averages with combined
water quality index
Figure 7 Total average macroinvertebrates and altitude profile of the river

12. 12
Figure 8 Correlations between total abundance of macroinvertebrate individuals for
all sampling station during the different campaign days and their averages with dissolved
oxygen water quality index
It is quite clear that the abundance of individuals correlates well with the water quality.
The higher the quality, the more abundant the presence of individuals. Figure 7 shows that
the river has a long stretch of low quality waters and scarcity of specimens in the altitudes
ranging from 1500 to 1350 m.a.sl, which entirely correspond to the dense populated areas of
the valley. This could also related to the fact that in a good part of that stretch the river runs
between concrete straight channels, lacking meanders and quiet ponds that could favor the
abundance of specimens. Another factor is that, in these stretches, the river is surrounded by
urban features (roads, buildings), which also can affect negatively any ecological activity.
Figure 9 shows how the river channelized near sampling station E7 [6]. The channeling goes
all the way from sampling station E3 to E11.
Figures 10 to 11 show correlations for two of the more abundant orders and genera found
in the study used as indicator of water quality.

13. 13
Figure 9 The Medellín river channelized near sampling station E7

14. 14
Figure 10 Correlations between abundance of Diptera Chironomidae larvae for all
sampling station during the different campaign days and their averages with combined and
dissolved-oxygen water quality indexes

15. 15
The Chironomidae (known as nonbiting midges or lake flies) comprise a family
belonging to the Diptera order and the Nematocera suborder. This is a large taxon of insects;
some estimates suggest well over 10.000 species worldwide. Their larval stages can be found
in almost any aquatic or semiaquatic habitat and form an important fraction of the
macrozoobenthos of most freshwater ecosystems. Larvae and pupae are important food items
for fish and for other aquatic organisms such as newts and many aquatic insects. The
abundances of individuals in this in this study family is clearly correlated with water quality,
and specially, with dissolved-oxygen water quality index.
Figure 11 Correlation between abundance of Haplotaxida for average of sampling
stations with combined water quality indexes
The Haplotaxida Order are pollution tolerant benthos, which belongs to Phylum
Annelida and Class Oligochaeta and are considered as biological indicator for polluted water
with high organic matter content. This is also the case for the situation in the Medellín river
as shown in figures 5 and 11 in this study.
5. Conclusions and recommendations
The existence of the type of information generated in studies like the ones carried by the
universities and AMVA [6] and the excellent research done in the region [9] for 40 years
give basis to compare with the expected recovery situations that will experiment the Medellín
River form 2019 on, once the new Bello Treatment Plant becomes operative. The present
article intents to approach the situation combining chemical and physical water quality
information with the abundances of biological species associated to the river, such as
macroinvertebrates, in such a way that the non-specialist can have a felling for it. The idea
here is to create consciousness and awareness to contribute to cleaning the river and
recovering it for recreation, public enjoyment and even for esthetic and beauty
contemplation.

16. 16
It is observed that there are clear correlations between water quality and the abundance
of macroinvertebrates. Two specific types can be used as specific indicators which are the
Chironomidae family, which should be abundant as indicator of good quality and the
Haplotaxida Order which should be absent. It is recommended to continuously keep track of
the abundances of these types, for example, by means of monthly sampling campaigns in
some eight stations: E1, E2, E7, E11, E13, E15, E18, E20, focused in taking samples of these
major macroinvertebrates, Dissolved Oxygen, temperature and conductivity. With this
information establish correlations similar to the ones presented here as indication of the
changes the river is experimenting.
The river as such, is a complex system. Besides the water quality and the ecological
equilibrium, abundance and lack of species associated with it, it is important to consider the
necessary abundance of trees, shrubs, grasses and bushes; birds, fish and non-aquatic insects.
In addition, to take into account the importance of having stretches of non-channelized shores
that favor the existence of life. This calls for coordinate efforts to understand the river and
adapt the city to its natural behavior as much as possible.
Acknowledgements
This article has been possible because there is an ample set of data provided by AMVA and
the four universities which did the original study and made it available for public use. The
author thanks Andrés Monzón Pineda for his help as a student assistant at INDISA to
digitalize and organize the available information.

17. 17
References
1. EPM. Informe de sostenibilidad. http://2015.sostenibilidadgrupoepm.com.co/nuestro-grupo/nuestra-
capacidad-instalada/agua-y-saneamiento/
2. http://www.water-technology.net/projects/bello-wastewater-treatment-plant-colombia/
3. UNIVERSIDAD DE ANTIOQUIA, UNIVERSIDAD PONTIFICIA BOLIVARIANA, UNIVERSIDAD
DE MEDELLÍN, UNIVERSIDAD NACIONAL. DISEÑO Y PUESTA EN MARCHA DE LA
SEGUNDA ETAPA DE LA RED DE MONITOREO AMBIENTAL EN LA CUENCA
HIDROGRÁFICA DEL RÍO ABURRÁ EN JURISDICCIÓN DEL ÁREA METROPOLITANA DEL
VALLE DE ABURRÁ. Medellín. 2007
4. Enrique Posada, et al. 2013, ESTABLECIMIENTO DE ÍNDICES DE CALIDAD AMBIENTAL DE
RÍOS CON BASES EN EL COMPORTAMIENTO DEL OXÍGENO DISUELTO Y DE LA
TEMPERATURA. APLICACIÓN AL CASO DEL RÍO MEDELLÍN, EN EL VALLE DE ABURRÁ EN
COLOMBIA. Dyna, año 80, Nro. 181, pp. 192-200. Medellín, octubre, 2013. ISSN 0012-7353
5. Protocol 1a: D-Net Method for Macroinvertebrate Collection. Acadia Learning. Participatory Science. In
http://participatoryscience.org/sites/default/files/ALProtocol1a_InvertebrateSamplingforHg_long.pdf
6. https://www.kienyke.com/noticias/gobernador-de-antioquia-pide-sanciones-a-quienes-contaminen-el-
rio-medellin
7. Holguin et al. Modelling the ecological impact of discharged urban waters upon receiving aquatic
ecosystems. A tropical lowland river case study: city Cali and the Cauca River in Colombia. International
Environmental Modelling and Software Society (iEMSs) 2010 International Congress on Environmental
Modelling and Software Modelling for Environment’s Sake, Fifth Biennial Meeting, Ottawa, Canada.
David A. Swayne, Wanhong Yang, A. A. Voinov, A. Rizzoli, T. Filatova (Eds.)
http://www.iemss.org/iemss2010/index.php?n=Main.Proceedings
8. Ruiz-Moreno el al.: Géneros de Chironominae. GUÍA PARA LA IDENTIFICACIÓN GENÉRICA DE
LARVAS DE QUIRONÓMIDOS (DIPTERA: CHIRONOMIDAE) DE LA SABANA DE BOGOTÁ.
111.SUBFAMILlAS TANYPODINAE, PODONOMINAE y DIAMESINAE. Caldasia 22 (1) 15-33,
1999
9. Gabriel Roldán-Pérez. 2016. Los macroinvertebrados como bioindicadores de la calidad del agua:cuatro
décadas de desarrollo en Colombia y Latinoamerica. Rev. Acad. Colomb. Cienc. Ex. Fis. Nat.
40(155):254-274, abril-junio de 2016. doi: http://dx.doi.org/10.18257/raccefyn.335
10. Paul Hanson, Monika Springer, Alonso Ramirez. Capítulo 1 Introducción a los grupos de
macroinvertebrados acuáticos. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 58 (Suppl. 4):
3-37, December 2010
11. Eduard Solà, 2008. Tricladita, Dugesia subtentaculata. Asexual specimen from Santa Fe, Montseny,
Catalonia. On line on
https://upload.wikimedia.org/wikipedia/commons/a/ac/Dugesia_subtentaculata_1.jpg
12. http://lakes.chebucto.org/ZOOBENTH/BENTHOS/xxv.html
13. https://commons.wikimedia.org/wiki/File:Placobdella_2013_001.jpg
14. http://naturalista.biodiversidad.co/observations/8271321
15. http://www.naturalista.mx/observations/9530209
16. https://www.asturnatura.com/familia/sphaeriidae.html
17. http://tolweb.org/Isotomidae/10331
18. https://hiveminer.com/Tags/taxonomy:order=ephemeroptera,victoria
19. Progomphus borealis, Gray Sand Dragon. Cave Creek, Maricopa Co., Arizona, USA in
https://commons.wikimedia.org/wiki/File:Progomphus_borealis.jpg
20. Perlidae (Golden Stones) Stonefly, in http://www.troutnut.com/specimen/860
21. D.S. Chandler. Rhagovelia obesa http://www.discoverlife.org/mp/20p?see=I_DSC174&res=640
22. Larva of the eastern dobsonfly, Corydalus cornutus (Linnaeus). Photograph by J.F. Butler, University of
Florida. In http://entnemdept.ufl.edu/creatures/misc/eastern_dobsonfly.htm
23. Coleoptera Elmidae Heterelmis larvae. In https://blancowateratlas.wordpress.com/biodiversity-
guide/animals/insectsinvertebrates/insectsinvertebrates/coleoptera-elmidae-heterelmis-larvae/
24. https://www.mdfrc.org.au/bugguide/resources/LepidopteraPyralidae_Lg.jpg
25. Nectopsyche larvae in.
https://www.waterbugkey.vcsu.edu/php/genuskey.php?idnum=15&o=Leptoceridae1L&type=genus

18. 18
26. Diptera Chironomidae larvae. In https://www.mdfrc.org.au
27. http://www.backyardnature.net/n/a/simulium.htm
28. Psychodidae - Clogmia albipunctata. By Hectonichus - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=22827766
29. Water mite (Hydracarina)
http://www.photomacrography.net/forum/viewtopic.php?t=10458&highlight=mite
30. I Palemonidi, Palaemonidae.
http://www.ittiofauna.org/webmuseum/decapodi/palaemonidae/index_big.htm